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49.25b1a23f.js

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(window.webpackJsonp=window.webpackJsonp||[]).push([[49],{277:function(t,s,n){"use strict";n.r(s);var e=n(0),a=Object(e.a)({},function(){var t=this,s=t.$createElement,n=t._self._c||s;return n("div",{staticClass:"content"},[t._m(0),t._v(" "),n("h4",{attrs:{id:"原文"}},[n("a",{staticClass:"header-anchor",attrs:{href:"#原文","aria-hidden":"true"}},[t._v("#")]),t._v(" "),n("a",{attrs:{href:"https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/instanceof",target:"_blank",rel:"noopener noreferrer"}},[t._v("原文"),n("OutboundLink")],1)]),t._v(" "),n("hr"),t._v(" "),t._m(1),t._v(" "),t._m(2),t._m(3),t._v(" "),t._m(4),t._v(" "),t._m(5),t._v(" "),t._m(6),t._v(" "),t._m(7),t._m(8),t._v(" "),n("p",[t._v("instanceof和多全局对象(多个frame或多个window之间的交互)")]),t._v(" "),t._m(9),t._v(" "),t._m(10),t._v(" "),n("p",[t._v("例子: 表明String对象和Date对象都属于Object类型")]),t._v(" "),t._m(11),t._v(" "),t._m(12),n("p",[t._v("演示mycar属于Car类型的同时又属于Object类型")]),t._v(" "),t._m(13),t._v(" "),t._m(14),t._m(15),t._v(" "),n("p",[t._v("确定一个对象在全局中是否为数组")]),t._v(" "),t._m(16)])},[function(){var t=this.$createElement,s=this._self._c||t;return s("h1",{attrs:{id:"instanceof运算符"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#instanceof运算符","aria-hidden":"true"}},[this._v("#")]),this._v(" instanceof运算符")])},function(){var t=this.$createElement,s=this._self._c||t;return s("h2",{attrs:{id:"语法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#语法","aria-hidden":"true"}},[this._v("#")]),this._v(" 语法")])},function(){var t=this.$createElement,s=this._self._c||t;return s("div",{staticClass:"language- line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-text"}},[s("code",[this._v("object instanceof constructor\n")])]),this._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[this._v("1")]),s("br")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("blockquote",[s("p",[this._v("参数"),s("br")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("ol",[s("li",[this._v("object 要检测的对象."),s("br")]),this._v(" "),s("li",[this._v("constructor  某个构造函数")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("h2",{attrs:{id:"描述"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#描述","aria-hidden":"true"}},[this._v("#")]),this._v(" 描述")])},function(){var t=this.$createElement,s=this._self._c||t;return s("blockquote",[s("p",[this._v("instanceof 运算符用来检测 constructor.prototype 是否存在于参数 object 的原型链上。")])])},function(){var t=this,s=t.$createElement,n=t._self._c||s;return n("div",{staticClass:"language- line-numbers-mode"},[n("pre",{pre:!0,attrs:{class:"language-text"}},[n("code",[t._v("// 定义构造函数\nfunction C(){}\nfunction D(){}\n\nvar o = new C();\n\n// true，因为 Object.getPrototypeOf(o) === C.prototype\no instanceof C;\n\n// false，因为 D.prototype不在o的原型链上\no instanceof D;\n\no instanceof Object; // true,因为Object.prototype.isPrototypeOf(o)返回true\nC.prototype instanceof Object // true,同上\n\nC.prototype = {};\nvar o2 = new C();\n\no2 instanceof C; // true\n\no instanceof C; // false,C.prototype指向了一个空对象,这个空对象不在o的原型链上.\n\nD.prototype = new C(); // 继承\nvar o3 = new D();\no3 instanceof D; // true\no3 instanceof C; // true\n")])]),t._v(" "),n("div",{staticClass:"line-numbers-wrapper"},[n("span",{staticClass:"line-number"},[t._v("1")]),n("br"),n("span",{staticClass:"line-number"},[t._v("2")]),n("br"),n("span",{staticClass:"line-number"},[t._v("3")]),n("br"),n("span",{staticClass:"line-number"},[t._v("4")]),n("br"),n("span",{staticClass:"line-number"},[t._v("5")]),n("br"),n("span",{staticClass:"line-number"},[t._v("6")]),n("br"),n("span",{staticClass:"line-number"},[t._v("7")]),n("br"),n("span",{staticClass:"line-number"},[t._v("8")]),n("br"),n("span",{staticClass:"line-number"},[t._v("9")]),n("br"),n("span",{staticClass:"line-number"},[t._v("10")]),n("br"),n("span",{staticClass:"line-number"},[t._v("11")]),n("br"),n("span",{staticClass:"line-number"},[t._v("12")]),n("br"),n("span",{staticClass:"line-number"},[t._v("13")]),n("br"),n("span",{staticClass:"line-number"},[t._v("14")]),n("br"),n("span",{staticClass:"line-number"},[t._v("15")]),n("br"),n("span",{staticClass:"line-number"},[t._v("16")]),n("br"),n("span",{staticClass:"line-number"},[t._v("17")]),n("br"),n("span",{staticClass:"line-number"},[t._v("18")]),n("br"),n("span",{staticClass:"line-number"},[t._v("19")]),n("br"),n("span",{staticClass:"line-number"},[t._v("20")]),n("br"),n("span",{staticClass:"line-number"},[t._v("21")]),n("br"),n("span",{staticClass:"line-number"},[t._v("22")]),n("br"),n("span",{staticClass:"line-number"},[t._v("23")]),n("br"),n("span",{staticClass:"line-number"},[t._v("24")]),n("br"),n("span",{staticClass:"line-number"},[t._v("25")]),n("br"),n("span",{staticClass:"line-number"},[t._v("26")]),n("br")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("blockquote",[s("p",[this._v("需要注意的是，如果表达式 obj instanceof Foo 返回true，则并不意味着该表达式会永远返回true，因为Foo.prototype属性的值有可能会改变，改变之后的值很有可能不存在于obj的原型链上，这时原表达式的值就会成为false。另外一种情况下，原表达式的值也会改变，就是改变对象obj的原型链的情况，虽然在目前的ES规范中，我们只能读取对象的原型而不能改变它，但借助于非标准的__proto__魔法属性，是可以实现的。比如执行obj."),s("strong",[this._v("proto")]),this._v(" = {}之后，obj instanceof Foo就会返回false了。")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("blockquote",[s("p",[this._v('在浏览器中，我们的脚本可能需要在多个窗口之间进行交互。多个窗口意味着多个全局环境，不同的全局环境拥有不同的全局对象，从而拥有不同的内置类型构造函数。这可能会引发一些问题。比如，表达式 [] instanceof window.frames[0].Array 会返回false，因为 Array.prototype !== window.frames[0].Array.prototype，因此你必须使用 Array.isArray(myObj) 或者 Object.prototype.toString.call(myObj) === "[object Array]"来判断myObj是否是数组。')])])},function(){var t=this.$createElement,s=this._self._c||t;return s("h2",{attrs:{id:"例子"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#例子","aria-hidden":"true"}},[this._v("#")]),this._v(" 例子")])},function(){var t=this.$createElement,s=this._self._c||t;return s("blockquote",[s("p",[this._v("下面的代码使用了instanceof来证明：String和Date对象同时也属于Object类型。")])])},function(){var t=this,s=t.$createElement,n=t._self._c||s;return n("div",{staticClass:"language- line-numbers-mode"},[n("pre",{pre:!0,attrs:{class:"language-text"}},[n("code",[t._v('var simpleStr = "This is a simple string";\nvar myString  = new String();\nvar newStr    = new String("String created with constructor");\nvar myDate    = new Date();\nvar myObj     = {};\n\nsimpleStr instanceof String; // returns false, 检查原型链会找到 undefined\nmyString  instanceof String; // returns true\nnewStr    instanceof String; // returns true\nmyString  instanceof Object; // returns true\n\nmyObj instanceof Object;    // returns true, despite an undefined prototype\n({})  instanceof Object;    // returns true, 同上\n\nmyString instanceof Date;   // returns false\n\nmyDate instanceof Date;     // returns true\nmyDate instanceof Object;   // returns true\nmyDate instanceof String;   // returns false\n')])]),t._v(" "),n("div",{staticClass:"line-numbers-wrapper"},[n("span",{staticClass:"line-number"},[t._v("1")]),n("br"),n("span",{staticClass:"line-number"},[t._v("2")]),n("br"),n("span",{staticClass:"line-number"},[t._v("3")]),n("br"),n("span",{staticClass:"line-number"},[t._v("4")]),n("br"),n("span",{staticClass:"line-number"},[t._v("5")]),n("br"),n("span",{staticClass:"line-number"},[t._v("6")]),n("br"),n("span",{staticClass:"line-number"},[t._v("7")]),n("br"),n("span",{staticClass:"line-number"},[t._v("8")]),n("br"),n("span",{staticClass:"line-number"},[t._v("9")]),n("br"),n("span",{staticClass:"line-number"},[t._v("10")]),n("br"),n("span",{staticClass:"line-number"},[t._v("11")]),n("br"),n("span",{staticClass:"line-number"},[t._v("12")]),n("br"),n("span",{staticClass:"line-number"},[t._v("13")]),n("br"),n("span",{staticClass:"line-number"},[t._v("14")]),n("br"),n("span",{staticClass:"line-number"},[t._v("15")]),n("br"),n("span",{staticClass:"line-number"},[t._v("16")]),n("br"),n("span",{staticClass:"line-number"},[t._v("17")]),n("br"),n("span",{staticClass:"line-number"},[t._v("18")]),n("br"),n("span",{staticClass:"line-number"},[t._v("19")]),n("br")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("blockquote",[s("p",[this._v("下面的代码创建了一个类型Car，以及该类型的对象实例mycar. instanceof运算符表明了这个mycar对象既属于Car类型，又属于Object类型。")])])},function(){var t=this,s=t.$createElement,n=t._self._c||s;return n("div",{staticClass:"language- line-numbers-mode"},[n("pre",{pre:!0,attrs:{class:"language-text"}},[n("code",[t._v('function Car(make, model, year) {\n  this.make = make;\n  this.model = model;\n  this.year = year;\n}\nvar mycar = new Car("Honda", "Accord", 1998);\nvar a = mycar instanceof Car;    // 返回 true\nvar b = mycar instanceof Object; // 返回 true\n')])]),t._v(" "),n("div",{staticClass:"line-numbers-wrapper"},[n("span",{staticClass:"line-number"},[t._v("1")]),n("br"),n("span",{staticClass:"line-number"},[t._v("2")]),n("br"),n("span",{staticClass:"line-number"},[t._v("3")]),n("br"),n("span",{staticClass:"line-number"},[t._v("4")]),n("br"),n("span",{staticClass:"line-number"},[t._v("5")]),n("br"),n("span",{staticClass:"line-number"},[t._v("6")]),n("br"),n("span",{staticClass:"line-number"},[t._v("7")]),n("br"),n("span",{staticClass:"line-number"},[t._v("8")]),n("br")])])},function(){var t=this.$createElement,s=this._self._c||t;return s("h3",{attrs:{id:"instanceof运算符在数组中的使用"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#instanceof运算符在数组中的使用","aria-hidden":"true"}},[this._v("#")]),this._v(" instanceof运算符在数组中的使用")])},function(){var t=this,s=t.$createElement,n=t._self._c||s;return n("div",{staticClass:"language-js line-numbers-mode"},[n("pre",{pre:!0,attrs:{class:"language-js"}},[n("code",[n("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" colors"),n("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),n("span",{pre:!0,attrs:{class:"token string"}},[t._v("'aa'")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),n("span",{pre:!0,attrs:{class:"token string"}},[t._v("'bb'")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),n("span",{pre:!0,attrs:{class:"token string"}},[t._v("'cc'")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),n("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//创建包含三个字符串的数组")]),t._v("\n"),n("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("colors "),n("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("instanceof")]),t._v(" "),n("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Array")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),n("span",{pre:!0,attrs:{class:"token function"}},[t._v("alert")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),n("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),n("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),t._v(" "),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),n("span",{pre:!0,attrs:{class:"token function"}},[t._v("alert")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),n("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),n("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),n("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//最后输出 1，说明该对象为数组")]),t._v("\n")])]),t._v(" "),n("div",{staticClass:"line-numbers-wrapper"},[n("span",{staticClass:"line-number"},[t._v("1")]),n("br"),n("span",{staticClass:"line-number"},[t._v("2")]),n("br"),n("span",{staticClass:"line-number"},[t._v("3")]),n("br"),n("span",{staticClass:"line-number"},[t._v("4")]),n("br"),n("span",{staticClass:"line-number"},[t._v("5")]),n("br"),n("span",{staticClass:"line-number"},[t._v("6")]),n("br"),n("span",{staticClass:"line-number"},[t._v("7")]),n("br")])])}],!1,null,null,null);s.default=a.exports}}]);
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