vuepress-theme-vdoing/assets/js/14.f19e1ed9.js

(window.webpackJsonp=window.webpackJsonp||[]).push([[14],{398:function(t,s,n){"use strict";n.r(s);var a=n(5),e=Object(a.a)({},(function(){var t=this,s=t._self._c;return s("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[s("h1",{attrs:{id:"new命令原理"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#new命令原理"}},[t._v("#")]),t._v(" new命令原理")]),t._v(" "),s("p",[t._v("使用new命令时，它后面的函数依次执行下面的步骤：")]),t._v(" "),s("ol",[s("li",[t._v("创建一个空对象，作为将要返回的实例对象。")]),t._v(" "),s("li",[t._v("将这个空对象的原型，指向构造函数的prototype属性。")]),t._v(" "),s("li",[t._v("将这个空对象赋值给函数内部的this关键字。")]),t._v(" "),s("li",[t._v("开始执行构造函数内部的代码。")]),t._v(" "),s("li",[t._v("如果构造函数内有返回值且为对象类型，则返回该对象，否则返回上面创建的实例对象。")])]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 构造函数")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("Person")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("name"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("age")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" name\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("age "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" age\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 自定义_new")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("_new")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 将 arguments 对象转为数组")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" args "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("slice")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("call")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("arguments"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 取出构造函数")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" constructor "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" args"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("shift")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 创建一个空对象，继承构造函数的 prototype 属性")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" context "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Object"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("create")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("constructor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("prototype"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 执行构造函数，并将context对象赋值给函数内部的this")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("constructor")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("apply")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("context"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" args"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 如果返回结果是对象，就直接返回，否则返回 context 对象")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typeof")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'object'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&&")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("?")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" context"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 自定义_new2")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("_new2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* 构造函数 */")]),t._v(" constructor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* 构造函数参数 */")]),t._v(" params"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 创建一个空对象，并继承构造函数的 prototype 属性")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" context "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Object"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("create")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("constructor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("prototype"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 执行构造函数，并将context对象赋值给函数内部的this")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("constructor")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("apply")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("context"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" params"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 如果返回结果是对象，就直接返回，否则返回 context 对象")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typeof")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'object'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&&")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("?")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" context"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// （当用户在构造函数内部自定义返回对象的话则使用该对象，否则返回context）")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 通过自定义_new 返回实例")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" actor "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("_new")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Person"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'张三'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("28")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nconsole"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("actor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 张三")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 通过自定义_new2 返回实例")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" actor2 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("_new2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Person"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'李四'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("29")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nconsole"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("actor2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 李四")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 通过new命令 返回实例")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" actor3 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Person")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'王五'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("30")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nconsole"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("actor3"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 王五")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br"),s("span",{staticClass:"line-number"},[t._v("14")]),s("br"),s("span",{staticClass:"line-number"},[t._v("15")]),s("br"),s("span",{staticClass:"line-number"},[t._v("16")]),s("br"),s("span",{staticClass:"line-number"},[t._v("17")]),s("br"),s("span",{staticClass:"line-number"},[t._v("18")]),s("br"),s("span",{staticClass:"line-number"},[t._v("19")]),s("br"),s("span",{staticClass:"line-number"},[t._v("20")]),s("br"),s("span",{staticClass:"line-number"},[t._v("21")]),s("br"),s("span",{staticClass:"line-number"},[t._v("22")]),s("br"),s("span",{staticClass:"line-number"},[t._v("23")]),s("br"),s("span",{staticClass:"line-number"},[t._v("24")]),s("br"),s("span",{staticClass:"line-number"},[t._v("25")]),s("br"),s("span",{staticClass:"line-number"},[t._v("26")]),s("br"),s("span",{staticClass:"line-number"},[t._v("27")]),s("br"),s("span",{staticClass:"line-number"},[t._v("28")]),s("br"),s("span",{staticClass:"line-number"},[t._v("29")]),s("br"),s("span",{staticClass:"line-number"},[t._v("30")]),s("br"),s("span",{staticClass:"line-number"},[t._v("31")]),s("br"),s("span",{staticClass:"line-number"},[t._v("32")]),s("br"),s("span",{staticClass:"line-number"},[t._v("33")]),s("br"),s("span",{staticClass:"line-number"},[t._v("34")]),s("br"),s("span",{staticClass:"line-number"},[t._v("35")]),s("br"),s("span",{staticClass:"line-number"},[t._v("36")]),s("br"),s("span",{staticClass:"line-number"},[t._v("37")]),s("br"),s("span",{staticClass:"line-number"},[t._v("38")]),s("br"),s("span",{staticClass:"line-number"},[t._v("39")]),s("br"),s("span",{staticClass:"line-number"},[t._v("40")]),s("br"),s("span",{staticClass:"line-number"},[t._v("41")]),s("br"),s("span",{staticClass:"line-number"},[t._v("42")]),s("br"),s("span",{staticClass:"line-number"},[t._v("43")]),s("br")])])])}),[],!1,null,null,null);s.default=e.exports}}]);