myBlogs_2/dist/assets/js/41.c3b1a78f.js

(window.webpackJsonp=window.webpackJsonp||[]).push([[41],{218:function(s,t,a){"use strict";a.r(t);var n=a(0),o=Object(n.a)({},function(){this.$createElement;this._self._c;return this._m(0)},[function(){var s=this,t=s.$createElement,a=s._self._c||t;return a("div",{staticClass:"content"},[a("h1",{attrs:{id:"匿名函数和闭包"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#匿名函数和闭包","aria-hidden":"true"}},[s._v("#")]),s._v(" 匿名函数和闭包")]),s._v(" "),a("p",[s._v("在计算机科学中，闭包是函数的非局部变量（自由变量）的引用环境。")]),s._v(" "),a("p",[s._v("包含自由变量的函数与为所有这些自由变量提供了变量绑定的环境一起,被称为闭包。")]),s._v(" "),a("p",[s._v("以下内容为学习笔记，来自李炎恢老师的课堂纪要。")]),s._v(" "),a("h2",{attrs:{id:"_1-匿名函数"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-匿名函数","aria-hidden":"true"}},[s._v("#")]),s._v(" 1.匿名函数")]),s._v(" "),a("p",[s._v("普通函数")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" 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"),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    age"),a("span",{attrs:{class:"token operator"}},[s._v("++")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" age"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" b "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//获得函数")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token function"}},[s._v("b")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//调用匿名函数")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token function"}},[s._v("b")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token 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"),a("span",{attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("5")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{attrs:{class:"token operator"}},[s._v("++")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    arr"),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n      "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" i"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" arr"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" b "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//得到函数数组")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//得到函数集合长度")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" i "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("0")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),a("span",{attrs:{class:"token operator"}},[s._v("<")]),s._v(" b"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{attrs:{class:"token operator"}},[s._v("++")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//输出每个函数的值，都是最后一个值")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" 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"),a("h3",{attrs:{id:"循环里包含匿名函数-改-1，自我执行匿名函数"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#循环里包含匿名函数-改-1，自我执行匿名函数","aria-hidden":"true"}},[s._v("#")]),s._v(" 循环里包含匿名函数-改 1，自我执行匿名函数")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" arr "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token 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punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("num"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n      "),a("span",{attrs:{class:"token comment"}},[s._v("//自我执行")]),s._v("\n      "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" num"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//并且传参")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  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operator"}},[s._v("<")]),s._v(" b"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{attrs:{class:"token operator"}},[s._v("++")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//这里返回的是数组，直接打印即可")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" 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"),a("h3",{attrs:{id:"循环里包含匿名函数-改-2，匿名函数下再做个匿名函"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#循环里包含匿名函数-改-2，匿名函数下再做个匿名函","aria-hidden":"true"}},[s._v("#")]),s._v(" 循环里包含匿名函数-改 2，匿名函数下再做个匿名函")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" arr "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token 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punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("num"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n      "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n        "),a("span",{attrs:{class:"token comment"}},[s._v("//直接返回值，改2 变成返回函数")]),s._v("\n        "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" num"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//原理和改1 一样")]),s._v("\n      "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" arr"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" b "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" i "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("0")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),a("span",{attrs:{class:"token operator"}},[s._v("<")]),s._v(" b"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{attrs:{class:"token operator"}},[s._v("++")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//这里通过b[i]()函数调用即可")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" 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1 和改 2 中，我们通过匿名函数自我执行，立即把结果赋值给 a[i]。每一个 i，是调用方通过按值传递的，所以最终返回的都是指定的递增的 i。而不是 box()函数里的 i。")]),s._v(" "),a("p",[s._v("关于 this 对象在闭包中使用 this 对象也可能会导致一些问题，this 对象是在运行时基于函数的执行环境绑定的，如果 this 在全局范围就是 window，如果在对象内部就指向这个对象。")]),s._v(" "),a("p",[s._v("而闭包却在运行时指向 window 的，因为闭包并不属于这个对象的属性或方法。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" user "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token string"}},[s._v("'The Window'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" obj "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    user "),a("span",{attrs:{class:"token punctuation"}},[s._v(":")]),s._v(" "),a("span",{attrs:{class:"token string"}},[s._v("'The Object'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(",")]),s._v("\n    getUserFunction "),a("span",{attrs:{class:"token punctuation"}},[s._v(":")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n        "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//闭包不属于obj，里面的this 指向window")]),s._v("\n            "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("this")]),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("user"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n        "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("obj"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function"}},[s._v("getUserFunction")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//The window")]),s._v("\n"),a("span",{attrs:{class:"token comment"}},[s._v("//可以强制指向某个对象")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("obj"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function"}},[s._v("getUserFunction")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function"}},[s._v("call")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("obj"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//The Object")]),s._v("\n"),a("span",{attrs:{class:"token comment"}},[s._v("//也可以从上一个作用域中得到对象")]),s._v("\ngetUserFunction "),a("span",{attrs:{class:"token punctuation"}},[s._v(":")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" that "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("this")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//从对象的方法里得对象")]),s._v("\n    "),a("span",{attrs:{class:"token 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"),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br")])]),a("h3",{attrs:{id:"内存泄漏"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#内存泄漏","aria-hidden":"true"}},[s._v("#")]),s._v(" 内存泄漏")]),s._v(" "),a("p",[s._v("由于 IE 的 JScript 对象和 DOM 对象使用不同的垃圾收集方式，因此闭包在 IE 中会导致一些问题。就是内存泄漏的问题，也就是无法销毁驻留在内存中的元素。以下代码有两个知识点还没有学习到，一个是 DOM，一个是事件。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" oDiv "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" document"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function"}},[s._v("getElementById")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token string"}},[s._v("'oDiv'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//oDiv 用完之后一直驻留在内存")]),s._v("\n  oDiv"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("onclick")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("oDiv"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("innerHTML"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//这里用oDiv 导致内存泄漏")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br")])]),a("p",[s._v("那么在最后应该将 oDiv 解除引用来避免内存泄漏。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" oDiv "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" document"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function"}},[s._v("getElementById")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token string"}},[s._v("'oDiv'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" text "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" oDiv"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("innerHTML"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  oDiv"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("onclick")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("text"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  oDiv "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("null")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//解除引用")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br")])]),a("p",[s._v("PS：如果并没有使用解除引用，那么需要等到浏览器关闭才得以释放。模仿块级作用域 JavaScript 没有块级作用域的概念。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("count"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" 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punctuation"}},[s._v("(")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//i 不会因为离开了for 块就失效")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token number"}},[s._v("2")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("count"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token 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function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token number"}},[s._v("2")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br")])]),a("p",[s._v("以上两个例子，说明 JavaScript 没有块级语句的作用域，if () {} for () {}等没有作用域，如果有，出了这个范围 i 就应该被销毁了。就算重新声明同一个变量也不会改变它的值。")]),s._v(" "),a("p",[a("code",[s._v("JavaScript")]),s._v("不会提醒你是否多次声明了同一个变量；遇到这种情况，它只会对后续的声明视而不见(如果初始化了，当然还会执行的)。使用模仿块级作用域可避免这个问题。")]),s._v(" "),a("h3",{attrs:{id:"模仿块级作用域-私有作用域"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#模仿块级作用域-私有作用域","aria-hidden":"true"}},[s._v("#")]),s._v(" 模仿块级作用域(私有作用域)")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token comment"}},[s._v("//这里是块级作用域")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token comment"}},[s._v("//使用块级作用域(私有作用域)改写")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("count"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" i "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("0")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),a("span",{attrs:{class:"token operator"}},[s._v("<")]),s._v(" count"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{attrs:{class:"token operator"}},[s._v("++")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//报错，无法访问")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token number"}},[s._v("2")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br")])]),a("p",[s._v("使用了块级作用域(私有作用域)后，匿名函数中定义的任何变量，都会在执行结束时被销毁。"),a("br"),s._v("\n这种技术经常在全局作用域中被用在函数外部，从而限制向全局作用域中添加过多的变量和函数。"),a("br"),s._v("\n一般来说，我们都应该尽可能少向全局作用域中添加变量和函数。在大型项目中，多人开发的时候，过多的全局变量和函数很容易导致命名冲突，引起灾难性的后果。"),a("br"),s._v("\n如果采用块级作用域(私有作用域)，每个开发者既可以使用自己的变量，又不必担心搞乱全局\n作用域。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" box "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{attrs:{class:"token number"}},[s._v("1")]),a("span",{attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("2")]),a("span",{attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("3")]),a("span",{attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("4")]),a("span",{attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("box"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//box 出来就不认识了")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br")])]),a("p",[s._v("在全局作用域中使用块级作用域可以减少闭包占用的内存问题，因为没有指向匿名函数的引用。只要函数执行完毕，就可以立即销毁其作用域链了。"),a("br"),s._v("\n私有变量"),a("code",[s._v("JavaScript")]),s._v("没有私有属性的概念；所有的对象属性都是公有的。"),a("br"),s._v("\n不过，却有一个私有变量的概念。任何在函数中定义的变量，都可以认为是私有变量，因为不能在函数的外部访问\n这些变量。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" age "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("100")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//私有变量，外部无法访问")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br")])]),a("p",[s._v("而通过函数内部创建一个闭包，那么闭包通过自己的作用域链也可以访问这些变量。而利用这一点，可以创建用于访问私有变量的公有方法。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("Box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" age "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("100")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//私有变量")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("run")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token comment"}},[s._v("//私有函数")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{attrs:{class:"token string"}},[s._v("'运行中...'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("this")]),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("get")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token comment"}},[s._v("//对外公共的特权方法")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" age "),a("span",{attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("run")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" box "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{attrs:{class:"token class-name"}},[s._v("Box")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token function"}},[s._v("alert")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("box"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token keyword"}},[s._v("get")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br")])]),a("h3",{attrs:{id:"可以通过构造方法传参来访问私有变量"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#可以通过构造方法传参来访问私有变量","aria-hidden":"true"}},[s._v("#")]),s._v(" 可以通过构造方法传参来访问私有变量")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("Person")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("value"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" user "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" value"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//这句其实可以省略")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("this")]),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("getUser")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" user"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("this")]),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("setUser")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("value"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    user "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" value"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("但是对象的方法，在多次调用的时候，会多次创建。可以使用静态私有变量来避免这个问题。"),a("br"),s._v("\n静态私有变量通过块级作用域(私有作用域)中定义私有变量或函数，同样可以创建对外公共的特权方\n法。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" age "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("100")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("run")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{attrs:{class:"token string"}},[s._v("'运行中...'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),a("span",{attrs:{class:"token function-variable function"}},[s._v("Box")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//构造方法")]),s._v("\n  Box"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("prototype"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("go")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token comment"}},[s._v("//原型方法")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" age "),a("span",{attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),a("span",{attrs:{class:"token function"}},[s._v("run")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token 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"),a("code",[s._v("function Box() {}")]),s._v(" 因为如果用后面这种，就变成私有函数了，无法在全局访问到了，所以使用了前面这种。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" user "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token string"}},[s._v("''")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token function-variable function"}},[s._v("Person")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token 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"),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" user"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  Person"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),s._v("prototype"),a("span",{attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{attrs:{class:"token function-variable function"}},[s._v("setUser")]),s._v(" "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),s._v("value"),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    user "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" value"),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("p",[s._v("使用了 prototype 导致方法共享了，而 user 也就变成静态属性了。(所谓静态属性，即共享于不同对象中的属性)。"),a("br"),s._v("\n模块模式之前采用的都是构造函数的方式来创建私有变量和特权方法。那么对象字面量方式就采用模块模式来创建。")]),s._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{attrs:{class:"token keyword"}},[s._v("var")]),s._v(" box "),a("span",{attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//字面量对象，也是单例对象")]),s._v("\n    age "),a("span",{attrs:{class:"token punctuation"}},[s._v(":")]),s._v(" "),a("span",{attrs:{class:"token number"}},[s._v("100")]),a("span",{attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//这是公有属性，将要改成私有")]),s._v("\n    run "),a("span",{attrs:{class:"token punctuation"}},[s._v(":")]),s._v(" "),a("span",{attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{attrs:{class:"token comment"}},[s._v("//这时公有函数，将要改成私有")]),s._v("\n        "),a("span",{attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{attrs:{class:"token string"}},[s._v("'运行中...'")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" 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