JavaScript 中继承实现方式归纳-守望者-AIR技术交流

破晓发表于 2016-8-11 15:09:22

JavaScript 中继承实现方式归纳

<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">本文同步自我的<a href="https://github.com/classicemi/araledoc/issues/10" target="_blank" style="text-decoration: none; color: rgb(49, 135, 219);">GitHub博客</a><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">不同于基于类的编程语言，如 C++ 和 Java，JavaScript 中的继承方式是基于原型的。同时由于 JavaScript 是一门非常灵活的语言，其实现继承的方式也非常多。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">首要的基本概念是关于构造函数和原型链的，父对象的构造函数称为<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Parent</code>，子对象的构造函数称为<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Child</code>，对应的父对象和子对象分别为<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">parent</code>和<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">child</code>。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">对象中有一个隐藏属性<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">[]</code>(注意不是<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">prototype</code>)，在 Chrome 中是<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">__proto__</code>，而在某些环境下则不可访问，它指向的是这个对象的原型。在访问任何一个对象的属性或方法时，首先会搜索本对象的所有属性，如果找不到的话则会根据<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">[]</code>沿着原型链逐步搜索其原型对象上的属性，直到找到为止，否则返回<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">undefined</code>。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">原型链继承：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">原型链是 JavaScript 中实现继承的默认方式，如果要让子对象继承父对象的话，最简单的方式是将子对象构造函数的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">prototype</code>属性指向父对象的一个实例：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function Parent() {}
function Child() {}
Child.prototype = new Parent()</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这个时候，<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Child</code>的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">prototype</code>属性被重写了，指向了一个新对象，但是这个新对象的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">constructor</code>属性却没有正确指向<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Child</code>，JS 引擎并不会自动为我们完成这件工作，这需要我们手动去将<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Child</code>的原型对象的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">constructor</code>属性重新指向<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Child</code>:<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">Child.prototype.constructor = Child</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">以上就是 JavaScript 中的默认继承机制，将需要重用的属性和方法迁移至原型对象中，而将不可重用的部分设置为对象的自身属性，但这种继承方式需要新建一个实例作为原型对象，效率上会低一些。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">原型继承（非原型链）：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">为了避免上一个方法需要重复创建原型对象实例的问题，可以直接将子对象构造函数的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">prototype</code>指向父对象构造函数的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">prototype</code>，这样，所有<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Parent.prototype</code>中的属性和方法也能被重用，同时不需要重复创建原型对象实例：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">Child.prototype = Parent.prototype
Child.prototype.constructor = Child</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">但是我们知道，在 JavaScript 中，对象是作为引用类型存在的，这种方法实际上是将<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Child.prototype</code>和<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Parent.prototype</code>中保存的指针指向了同一个对象，因此，当我们想要在子对象原型中扩展一些属性以便之后继续继承的话，父对象的原型也会被改写，因为这里的原型对象实例始终只有一个，这也是这种继承方式的缺点。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">临时构造器继承：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">为了解决上面的问题，可以借用一个临时构造器起到一个中间层的作用，所有子对象原型的操作都是在临时构造器的实例上完成，不会影响到父对象原型：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">var F = function() {}
F.prototype = Parent.prototype
Child.prototype = new F()
Child.prototype.constructor = Child</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">同时，为了可以在子对象中访问父类原型中的属性，可以在子对象构造器上加入一个指向父对象原型的属性，如<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">uber</code>，这样，可以在子对象上直接通过<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">child.constructor.uber</code>访问到父级原型对象。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">我们可以将上面的这些工作封装成一个函数，以后调用这个函数就可以方便实现这种继承方式了：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function extend(Child, Parent) {
var F = function() {}
F.prototype = Parent.prototype
Child.prototype = new F()
Child.prototype.constructor = Child
Child.uber = Parent.prototype
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">然后就可以这样调用：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">extend(Dog, Animal)</code></pre><h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">属性拷贝：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这种继承方式基本没有改变原型链的关系，而是直接将父级原型对象中的属性全部复制到子对象原型中，当然，这里的复制仅仅适用于基本数据类型，对象类型只支持引用传递。<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function extend2(Child, Parent) {
var p = Parent.prototype
var c = Child.prototype
for (var i in p) {
 c[i] = p[i]
}
c.uber = p
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这种方式对部分原型属性进行了重建，构建对象的时候效率会低一些，但是能够减少原型链的查找。不过我个人觉得这种方式的优点并不明显。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">对象间继承：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">除了基于构造器间的继承方法，还可以抛开构造器直接进行对象间的继承。即直接进行对象属性的拷贝，其中包括浅拷贝和深拷贝。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">浅拷贝： 接受要继承的对象，同时创建一个新的空对象，将要继承对象的属性拷贝至新对象中并返回这个新对象：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function extendCopy(p) {
var c = {}
for (var i in p) {
 c[i] = p[i]
}
c.uber = p
return c
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">拷贝完成之后对于新对象中需要改写的属性可以进行手动改写。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">深拷贝： 浅拷贝的问题也显而易见，它不能拷贝对象类型的属性而只能传递引用，要解决这个问题就要使用深拷贝。深拷贝的重点在于拷贝的递归调用，检测到对象类型的属性时就创建对应的对象或数组，并逐一复制其中的基本类型值。<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function deepCopy(p, c) {
c = c || {}
for (var i in p) {
 if (p.hasOwnProperty(i)) {
 if (typeof p[i] === 'object') {
 c[i] = Array.isArray(p[i]) ? [] : {}
 deepCopy(p[i], c[i])
 } else {
 c[i] = p[i]
 }
 }
}
return c
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">其中用到了一个 ES5 的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Array.isArray()</code>方法用于判断参数是否为数组，没有实现此方法的环境需要自己手动封装一个 shim。<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">Array.isArray = function(p) {
return p instanceof Array
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">但是使用<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">instanceof</code>操作符无法判断来自不同框架的数组变量，但这种情况比较少。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">原型继承：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">借助父级对象，通过构造函数创建一个以父级对象为原型的新对象：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function object(o) {
var n
function F() {}
F.prototype = o
n = new F()
n.uber = o
return n
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这里，直接将父对象设置为子对象的原型，ES5 中的 <code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Object.create()</code>方法就是这种实现方式。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">原型继承和属性拷贝混用：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">原型继承方法中以传入的父对象为原型构建子对象，同时还可以在父对象提供的属性之外额外传入需要拷贝属性的对象：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function ojbectPlus(o, stuff) {
var n
function F() {}
F.prototype = o
n = new F()
n.uber = o

for (var i in stuff) {
 n[i] = stuff[i]
}
return n
}</code></pre><h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">多重继承：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这种方式不涉及原型链的操作，传入多个需要拷贝属性的对象，依次进行属性的全拷贝：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function multi() {
var n = {}, stuff, i = 0,
 len = arguments.length
for (i = 0; i < len; i++) {
 stuff = arguments[i]
 for (var key in stuff) {
 n[i] = stuff[i]
 }
}
return n
}</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">根据对象传入的顺序依次进行拷贝，也就是说，如果后传入的对象包含和前面对象相同的属性，后者将会覆盖前者。<h2 style="font-size: 26px; margin-top: 20px; margin-bottom: 20px; counter-reset: section 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">构造器借用：</h2><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">JavaScript中的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">call()</code>和<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">apply()</code>方法非常好用，其改变方法执行上下文的功能在继承的实现中也能发挥作用。所谓构造器借用是指在子对象构造器中借用父对象的构造函数对<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">this</code>进行操作：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">function Parent() {}
Parent.prototype.name = 'parent'

function Child() {
Parent.apply(this, arguments)
}
var child = new Child()
console.log(child.name)</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这种方式的最大优势就是，在子对象的构造器中，是对子对象的自身属性进行完全的重建，引用类型的变量也会生成一个新值而不是一个引用，所以对子对象的任何操作都不会影响父对象。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">而这种方法的缺点在于，在子对象的构建过程中没有使用过<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">new</code>操作符，因此子对象不会继承父级原型对象上的任何属性，在上面的代码中，<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">child</code>的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">name</code>属性将会是<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">undefined</code>。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">要解决这个问题，可以再次手动将子对象构造器原型设为父对象的实例：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">Child.prototype = new Parent()</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">但这样又会带来另一个问题，即父对象的构造器会被调用两次，一次是在父对象构造器借用过程中，另一次是在继承原型过程中。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">要解决这个问题，就要去掉一次父对象构造器的调用，构造器借用不能省略，那么只能去掉后一次调用，实现继承原型的另一方法就是迭代复制：<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">extend2(Child, Parent)</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">使用之前实现的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">extend2()</code>方法即可。

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守望者--AIR技术交流's Archiver

JavaScript 中继承实现方式归纳