JavaScript的深拷贝的实现

JavaScript的数据类型

简单数据类型

string
number
boolean
function
null
undefined

复杂数据类型

String
Number
Boolean
Function
Date
Array
RegExp
Object

各种类型的深复制方式：

先来看看简单类型的复制方式：

//string

var s1 = 'abc';

var s2 = s1;

s2 = 'ccc';

console.log(s1);

//number

var n1 = 12.1;

var n2 = n1;

n2 = 7410;

console.log(n1);

//boolean

var b1 = true;

var b2 = b1;

b2 = false;

console.log(b1);

//null

var nu1 = null;

var nu2 = nu1;

nu2 = 'abc';

console.log(nu1);

//undefined

var u1 = undefined;

var u2 = u1;

u2 = 'abc';

console.log(u1);

从以上的代码可以看出，简单类型，只需要直接赋值就是深复制了。但是也有一个例外，那就是function。

接着来看看String、Number、Boolean、Date的深复制：

//String

var s1 = new String('s1');

var s2 = new String(s1);

console.log(s2);

//Number

var n1 = new Number('1');

var n2 = new Number(n1);

console.log(n2);

//Boolean

var b1 = new Boolean(1);

var b2 = new Boolean(b1);

console.log(b2);

//Date

var d1 = new Date();

var d2 = new Date(d1);

console.log(d2);

除以上的做法之外，还需要对实例属性进行拷贝。那么剩下的Function、function、RegExp和Array还有Object又该怎么拷贝呢？这几个比较特殊，我们一个一个来：

对于Function和function的深拷贝，我们可以按照如下的方式来做：

var f1 = new Function('a', 'console.log("f1" + a);');

var f2 = function(b){console.log('f2' + b);};

//通过toString获取源代码(有浏览器兼容问题)

var code = f1.toString();

//利用eval进行复制

var f1_copy = (function(functionCode){

  eval('var f = ' + functionCode);

  return f;

})(code);

f1_copy('abc');

//当然f2也可以用同样的方式来复制。

接着，我们来看下RegExp，可以同样同时eval来执行拷贝，也可以使用如下方式：

var reg1 = /abc/g;

var reg2 = new RegExp('abc', 'gmi');

var reg1_copy = (function(reg){

  var pattern = reg.valueOf();

  var flags = (pattern.global ? 'g' : '') +

    (pattern.ignorecase ? 'i' : '') + (pattern.multiline ? 'm' : '');

  return new RegExp(pattern.source, flags);

})(reg1);

最后，我们来说一说Array的复制，有的人可以说，直接用slice复制一份出来就是了，那我们来看看，是否真的达到效果的呢？

var o = {name: 'Jay'};

var arr1 = [o, '22', 1];

var arr2 = arr1.slice(0);

arr2[0].name = 'Arr2';

console.log(arr1[0].name);

很简短的代码，直接就把slice抛弃了，slice只能保证Array是新的，并不意味着内部的元素是深拷贝的，那么如何做呢？就是遍历元素，对每个元素进行深拷贝了。代码如下：

var o = {name: 'Jay'};

var arr1 = [o, '22', 1];

var arr2 = [];

for(var i = 0, len = arr1.length; i < len; i++){

  //注意，deepClone还未实现

  arr2.push(deepClone(arr1[i]));

}

以上对针对不同的类型，特殊的代码，那么如何来拷贝实例属性呢？代码如下：

var o = {p1: '1', p2: 2, p3: function(){}};

var copy = {};

for(var p in o){

  //注意deepClone还未实现

  copy[p] = deepClone(o[p]);

}

注意：针对复杂类型，还需要同时copy.constructor = source.constructor来保证构造函数一致。

最终的深复制代码

通过以上的分析与代码示例，那么我们最终的代码又是怎样的呢？详细代码如下：

//自调用函数，防御性编程

;

(function (window) {

  'use strict';

  function getCustomType(obj) {

    var type = typeof obj,

      resultType = 'object';

    //简单类型

    if (type !== 'object' || obj === null) {

      resultType = 'simple';

    } else if (obj instanceof String || obj instanceof Number || obj instanceof Boolean || obj instanceof Date) {

      resultType = 'complex';

    } else if (obj instanceof Function) {

      resultType = 'function';

    } else if (obj instanceof RegExp) {

      resultType = 'regexp';

    } else if (obj instanceof Array) {

      resultType = 'array';

    }

    return resultType;

  }

  function cloneProperties(dest, source) {

    dest.constructor = source.constructor;

    for (var p in source) {

      dest[p] = deepClone(source[p]);

    }

    return dest;

  }

  function cloneSimple(obj) {

    return obj;

  }

  function cloneComplex(obj) {

    var result = new obj.constructor(obj);

    return cloneProperties(result);

  }

  function cloneFunction(obj) {

    var funCopy = (function (f) {

      eval('var abcdefg_$$$$ = ' + obj.toString());

      return abcdefg_$$$$;

    })(obj);

    return cloneProperties(funCopy);

  }

  function cloneRegExp(obj) {

    var pattern = obj.valueOf();

    var flags = (pattern.global ? 'g' : '') +

      (pattern.ignorecase ? 'i' : '') + (pattern.multiline ? 'm' : '');

    var reg = new RegExp(pattern.source, flags);

    return cloneProperties(reg);

  }

  function cloneArray(obj) {

    var resultArr = [];

    for (var i = 0, len = obj.length; i < len; i++) {

      resultArr.push(deepClone(obj[i]));

    }

    for (var p in obj) {

      if (typeof p === 'number' && p < len) {

        continue;

      }

      resultArr[p] = deepClone(obj[p]);

    }

    return resultArr;

  }

  function cloneObject(obj) {

    var result = {};

    result.constructor = obj.constructor;

    for (var p in obj) {

      result[p] = deepClone(obj[p]);

    }

    return result;

  }

  function deepClone(obj) {

    var f = undefined;

    switch (getCustomType(obj)) {

    case 'simple':

      f = cloneSimple;

      break;

    case 'complex':

      f = cloneComplex;

      break;

    case 'function':

      f = cloneFunction;

      break;

    case 'regexp':

      f = cloneRegExp;

      break;

    case 'array':

      f = cloneArray;

      break;

    case 'object':

      f = cloneObject;

      break;

    }

    return f.call(undefined, obj);

  }

  //挂载到window对象上

  window.deepClone = deepClone;

})(window);

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-->