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"),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br"),a("span",{staticClass:"line-number"},[t._v("9")]),a("br"),a("span",{staticClass:"line-number"},[t._v("10")]),a("br"),a("span",{staticClass:"line-number"},[t._v("11")]),a("br")])]),a("p",[t._v("从技术上来讲，在 JS 中，每个 function 都是闭包，因为它总是能访问在它外部定义的数据。")]),t._v(" "),a("h2",{attrs:{id:"写给初级-js-程序员的-javascript-闭包-译"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#写给初级-js-程序员的-javascript-闭包-译"}},[t._v("#")]),t._v(" 写给初级 JS 程序员的 JavaScript 闭包(译)")]),t._v(" "),a("p",[a("a",{attrs:{href:"http://web.archive.org/web/20080209105120/http:/blog.morrisjohns.com/javascript_closures_for_dummies",target:"_blank",rel:"noopener noreferrer"}},[t._v("原文链接"),a("OutboundLink")],1)]),t._v(" "),a("h3",{attrs:{id:"闭包不是魔术"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#闭包不是魔术"}},[t._v("#")]),t._v(" 闭包不是魔术")]),t._v(" "),a("p",[t._v("这个页面解释了 closures，以便程序员可以理解它们 - 使用有效的 JavaScript 代码。它不是用于古茹或功能程序员。"),a("br"),t._v("\n一旦核心概念被解构，闭包不难理解。然而，他们不可能通过阅读任何学术论文或面向学术的信息来了解他们！"),a("br"),t._v("\n本文主要面向有主流语言编程经验的程序员，他们可以阅读以下 JavaScript 函数：")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayHello")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("name")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" text "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello '")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("say")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("text"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("say")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayHello")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Joe'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br")])]),a("h3",{attrs:{id:"闭包的实例"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#闭包的实例"}},[t._v("#")]),t._v(" 闭包的实例")]),t._v(" "),a("p",[t._v("两句话摘要："),a("br"),t._v("\n它是一个可以引用其范围内的变量（在第一次声明时），被赋值给变量，作为参数传递给函数或作为函数结果返回的表达式。"),a("br"),t._v("\n闭包是一个堆栈框架，当函数开始执行时被分配，并且在函数返回之后不被释放（就好像“堆栈框架”在堆上分配而不是堆栈！）。")]),t._v(" "),a("p",[t._v("以下代码返回对函数的引用：")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayHello2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("name")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" text "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello '")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Local variable")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("say")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("text"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" say"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" say2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayHello2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Bob'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("say2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// logs "Hello Bob"')]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br"),a("span",{staticClass:"line-number"},[t._v("9")]),a("br")])]),a("p",[t._v("大多数 JavaScript 程序员将会理解在上面的代码中如何将一个函数的引用返回给一个变量。如果你没有，那么你需要在你可以学习闭包。AC 程序员会认为函数返回一个指向函数的指针，变量 sayAlert 和 say2 都是指向函数的指针。")]),t._v(" "),a("p",[t._v("在指向函数的 C 指针和对函数的 JavaScript 引用之间存在关键的区别。在 JavaScript 中，您可以将函数引用变量看作具有指向函数的指针 以及指向闭包的隐藏指针。")]),t._v(" "),a("p",[t._v("上面的代码有一个闭包，因为匿名函数 function（）{alert（text）; } 在另一个函数中声明，在这个例子中为 sayHello2（）。在 JavaScript 中，如果在另一个函数中使用 function 关键字，则要创建一个闭包。")]),t._v(" "),a("p",[t._v("在 C 和大多数其他常用语言函数返回后，所有的局部变量不再可访问，因为堆栈帧被销毁。")]),t._v(" "),a("p",[t._v("在 JavaScript 中，如果在另一个函数中声明一个函数，那么在从调用的函数返回后，局部变量仍然可以访问。这是上面演示的，因为我们调用函数 say2（）; 之后我们从 sayHello2（）返回。请注意，我们调用的代码引用变量 text，它是函数 sayHello2（）的局部变量。")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("text"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Output of say2.toString();")]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br")])]),a("p",[t._v("看看输出 say2.toString()，我们可以看到代码引用的变量 text。匿名函数可以引用 text 保存值的值'Hello Bob'，因为局部变量 sayHello2()保存在闭包中。")]),t._v(" "),a("p",[t._v("神奇的是，在 JavaScript 中，函数引用还具有对其创建的闭包的秘密引用 - 类似于如何委托是方法指针加上对对象的秘密引用。")]),t._v(" "),a("hr"),t._v(" "),a("h3",{attrs:{id:"更多例子"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#更多例子"}},[t._v("#")]),t._v(" 更多例子")]),t._v(" "),a("p",[t._v("出于某种原因，当你阅读关于它们的闭包似乎真的很难理解，但当你看到一些例子，你可以点击他们的工作（它花了我一段时间）。我建议仔细阅读示例，直到你了解它们如何工作。如果你开始使用闭包没有完全了解它们如何工作，你很快就会创建一些非常古怪的错误！")]),t._v(" "),a("h4",{attrs:{id:"例-3"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#例-3"}},[t._v("#")]),t._v(" 例 3")]),t._v(" "),a("p",[t._v("此示例显示不复制局部变量 - 它们通过引用保留。它是一种像在外部函数退出时在内存中保留一个堆栈框架！")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("say667")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Local variable that ends up within closure")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("42")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("say")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("num"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n num"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" say"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" sayNumber "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("say667")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayNumber")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// logs 43")]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br"),a("span",{staticClass:"line-number"},[t._v("9")]),a("br"),a("span",{staticClass:"line-number"},[t._v("10")]),a("br"),a("span",{staticClass:"line-number"},[t._v("11")]),a("br")])]),a("h4",{attrs:{id:"例-4"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#例-4"}},[t._v("#")]),t._v(" 例 4")]),t._v(" "),a("p",[t._v("所有三个全局函数具有对同一闭包的公共引用，因为它们都在单个调用中声明 setupSomeGlobals()。"),a("br")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" gLogNumber"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" gIncreaseNumber"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" gSetNumber"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("setupSomeGlobals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Local variable that ends up within closure")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("42")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Store some references to functions as global variables")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("gLogNumber")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("num"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("gIncreaseNumber")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n num"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("gSetNumber")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("x")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("setupSomeGlobals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("gIncreaseNumber")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("gLogNumber")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 43")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("gSetNumber")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("gLogNumber")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 5")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" oldLog "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" gLogNumber"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("setupSomeGlobals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("gLogNumber")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 42")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("oldLog")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 5")]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br"),a("span",{staticClass:"line-number"},[t._v("9")]),a("br"),a("span",{staticClass:"line-number"},[t._v("10")]),a("br"),a("span",{staticClass:"line-number"},[t._v("11")]),a("br"),a("span",{staticClass:"line-number"},[t._v("12")]),a("br"),a("span",{staticClass:"line-number"},[t._v("13")]),a("br"),a("span",{staticClass:"line-number"},[t._v("14")]),a("br"),a("span",{staticClass:"line-number"},[t._v("15")]),a("br"),a("span",{staticClass:"line-number"},[t._v("16")]),a("br"),a("span",{staticClass:"line-number"},[t._v("17")]),a("br"),a("span",{staticClass:"line-number"},[t._v("18")]),a("br"),a("span",{staticClass:"line-number"},[t._v("19")]),a("br"),a("span",{staticClass:"line-number"},[t._v("20")]),a("br"),a("span",{staticClass:"line-number"},[t._v("21")]),a("br"),a("span",{staticClass:"line-number"},[t._v("22")]),a("br"),a("span",{staticClass:"line-number"},[t._v("23")]),a("br"),a("span",{staticClass:"line-number"},[t._v("24")]),a("br"),a("span",{staticClass:"line-number"},[t._v("25")]),a("br"),a("span",{staticClass:"line-number"},[t._v("26")]),a("br"),a("span",{staticClass:"line-number"},[t._v("27")]),a("br"),a("span",{staticClass:"line-number"},[t._v("28")]),a("br")])]),a("p",[t._v("这三个函数具有对同一闭包的共享访问 - setupSomeGlobals()当定义三个函数时的局部变量。"),a("br"),t._v("\n注意，在上面的例子中，如果 setupSomeGlobals()再次调用，则创建一个新的闭包（stack-frame！）。老 gLogNumber，gIncreaseNumber，gSetNumber 变量将覆盖新的具有新功能关闭。（在 JavaScript 中，当你声明另一个函数内的函数，里面的功能（s）是/再次重新创建每个外部函数被调用时）。")]),t._v(" "),a("h4",{attrs:{id:"例-5"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#例-5"}},[t._v("#")]),t._v(" 例 5")]),t._v(" "),a("p",[t._v("这是一个真正的困扰，许多人，所以你需要了解它。要非常小心，如果你在一个循环中定义一个函数：从闭包的局部变量不会像你可能会想的那样。")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("buildList")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("list")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" result "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("length"),a("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("item "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("' '")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),t._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" result"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("testList")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" fnlist "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("buildList")]),a("span",{pre:!0,attrs:{class:"token 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"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" j "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v(" fnlist"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("length"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" j"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n fnlist"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),t._v("j"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("testList")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('//logs "item2 undefined" 3 times')]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br"),a("span",{staticClass:"line-number"},[t._v("9")]),a("br"),a("span",{staticClass:"line-number"},[t._v("10")]),a("br"),a("span",{staticClass:"line-number"},[t._v("11")]),a("br"),a("span",{staticClass:"line-number"},[t._v("12")]),a("br"),a("span",{staticClass:"line-number"},[t._v("13")]),a("br"),a("span",{staticClass:"line-number"},[t._v("14")]),a("br"),a("span",{staticClass:"line-number"},[t._v("15")]),a("br"),a("span",{staticClass:"line-number"},[t._v("16")]),a("br"),a("span",{staticClass:"line-number"},[t._v("17")]),a("br"),a("span",{staticClass:"line-number"},[t._v("18")]),a("br"),a("span",{staticClass:"line-number"},[t._v("19")]),a("br"),a("span",{staticClass:"line-number"},[t._v("20")]),a("br")])]),a("p",[t._v("在结果数组中添加一个对匿名函数的引用三次。如果你不熟悉匿名函数， 就如：")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("pointer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("item "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("' '")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token 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"),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br")])]),a("p",[t._v("注意，当运行示例时，“item2 undefined”会提醒三次！ 这是因为就像前面的例子一样，buildList 的局部变量只有一个闭包。 当在 fnlist [j]（）上调用匿名函数时; 它们都使用相同的单个闭包，并且它们使用该闭包内的 i 和项的当前值（其中 i 具有值 3，因为循环已完成，并且项具有值'item2'）。 注意，我们从 0 索引，因此项目的值为 item2。 并且 i ++将 i 增加到值 3。")]),t._v(" "),a("h4",{attrs:{id:"例-6"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#例-6"}},[t._v("#")]),t._v(" 例 6")]),t._v(" "),a("p",[t._v("此示例显示，闭包包含在退出前在外部函数中声明的任何局部变量。 注意，变量 alice 实际上是在匿名函数之后声明的。 匿名函数首先声明; 并且当调用该函数时，它可以访问 alice 变量，因为 alice 在同一范围内（JavaScript 变量提升）。 另外 sayAlice（）（）只是直接调用从 sayAlice（）返回的函数引用 - 它完全与以前做过的相同，但没有临时变量。")]),t._v(" "),a("div",{staticClass:"language-js line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayAlice")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("say")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("alice"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Local variable that ends up within closure")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" alice "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello Alice'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" say"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sayAlice")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// logs "Hello Alice"')]),t._v("\n")])]),t._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[t._v("1")]),a("br"),a("span",{staticClass:"line-number"},[t._v("2")]),a("br"),a("span",{staticClass:"line-number"},[t._v("3")]),a("br"),a("span",{staticClass:"line-number"},[t._v("4")]),a("br"),a("span",{staticClass:"line-number"},[t._v("5")]),a("br"),a("span",{staticClass:"line-number"},[t._v("6")]),a("br"),a("span",{staticClass:"line-number"},[t._v("7")]),a("br"),a("span",{staticClass:"line-number"},[t._v("8")]),a("br"),a("span",{staticClass:"line-number"},[t._v("9")]),a("br")])]),a("p",[t._v("Tricky：还要注意，say 变量也在闭包内，并且可以被可能被声明的任何其他函数访问 sayAlice()，或者它可以在内部函数内被递归地访问。")]),t._v(" "),a("h4",{attrs:{id:"例-7"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#例-7"}},[t._v("#")]),t._v(" 例 7")]),t._v(" "),a("p",[t._v("最后一个例子显示每个调用为局部变量创建一个单独的闭包。 每个函数声明没有单个闭包。 每个函数的调用都有一个闭包。")]),t._v(" "),a("div",{staticClass:"language-js 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4;")]),t._v("\nobj"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("someVar"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("fn1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// num: 7; anArray: 1,2,3,5,7; ref.someVar: 5;")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("fn2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token 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"),a("h4",{attrs:{id:"概要"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#概要"}},[t._v("#")]),t._v(" 概要")]),t._v(" "),a("p",[t._v("如果一切似乎完全不清楚，那么最好的办法是玩的例子。阅读解释比理解示例困难得多。我对闭包和堆栈框架等的解释在技术上是不正确的 - 它们是用于帮助理解的粗略简化。一旦基本的想法是 grokked，你可以提取细节后。")]),t._v(" "),a("h4",{attrs:{id:"总结"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#总结"}},[t._v("#")]),t._v(" 总结:")]),t._v(" "),a("p",[t._v("1.当你 function 在另一个函数里面使用时，使用闭包。")]),t._v(" "),a("p",[t._v("2.每当在函数中使用 eval（）时，都会使用闭包。 eval 的文本可以引用函数的局部变量，在 eval 中甚至可以使用 eval（'var foo = ...'）创建新的局部变量")]),t._v(" "),a("p",[t._v("3.当在函数中使用新的 Function（...）（Function 构造函数）时，它不会创建闭包。 （新函数不能引用外层函数的局部变量。）")]),t._v(" "),a("p",[t._v("4.JavaScript 中的闭包就像保留所有局部变量的副本，就像函数退出时一样。")]),t._v(" "),a("p",[t._v("5.最好是认为闭包始终只创建一个函数的入口，局部变量将添加到闭包中。")]),t._v(" "),a("p",[t._v("6.每次调用具有闭包的函数时，都会保存一组新的局部变量（假定函数在其中包含函数声明，并且对该函数的引用要么返回，要么以某种方式保留外部引用 ）。")]),t._v(" "),a("p",[t._v("7.两个函数可能看起来像它们具有相同的源文本，但是具有完全不同的行为，因为它们的“隐藏”闭包。 我不认为 JavaScript 代码实际上可以找出一个函数引用是否有闭包。")]),t._v(" "),a("p",[t._v("8.如果你试图做任何动态源代码修改（例如：myFunction = Function（myFunction.toString（）。replace（/ Hello /，'Hola'））;），如果 myFunction 是一个闭包 当然，你永远不会想到在运行时做源代码字符串替换，但...）。")]),t._v(" "),a("p",[t._v("9.可以在函数内的函数声明中获得函数声明 - 你可以在多个级别获得闭包。")]),t._v(" "),a("p",[t._v("10.我认为通常闭包是函数和捕获的变量的术语。 注意，我在本文中不使用这个定义！")]),t._v(" "),a("p",[t._v("11.我怀疑 JavaScript 中的闭包不同于通常在函数式语言中发现的闭包。")]),t._v(" "),a("h4",{attrs:{id:"链接"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#链接"}},[t._v("#")]),t._v(" 链接:")]),t._v(" "),a("p",[t._v("1.Douglas Crockford 的模拟"),a("a",{attrs:{href:"http://www.crockford.com/javascript/private.html",target:"_blank",rel:"noopener noreferrer"}},[t._v("私有属性和一个对象的私有方法"),a("OutboundLink")],1),t._v("，使用闭包。")]),t._v(" "),a("p",[t._v("2.一个伟大的解释如何闭包可以导致"),a("a",{attrs:{href:"https://www.codeproject.com/Articles/12231/Memory-Leakage-in-Internet-Explorer-revisited",target:"_blank",rel:"noopener noreferrer"}},[t._v("内存泄漏在 IE"),a("OutboundLink")],1),t._v("如果你不小心。")]),t._v(" "),a("h4",{attrs:{id:"感谢"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#感谢"}},[t._v("#")]),t._v(" 感谢")]),t._v(" "),a("p",[t._v("If you have just learnt closures (here or elsewhere!), "),a("br"),t._v("\n如果你刚刚学会了闭包（在这里或其他地方！），")]),t._v(" "),a("p",[t._v("then I am interested in any feedback from you about any changes you might suggest that could make this article clearer."),a("br"),t._v("\n那么我对你提出的任何有关你可能提出的任何可能使本文更清晰的变化的反馈感兴趣。")]),t._v(" "),a("p",[t._v("Send an email to morrisjohns.com (morris_closure @). Please note that I am not a guru on JavaScript - nor on closures.\n发送电子邮件至morrisjohns.com（morris_closure @）。 请注意，我不是JavaScript的大师 - nor on closures.")])])}),[],!1,null,null,null);s.default=e.exports}}]);
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