js对象深拷贝和淺拷贝

深拷贝和浅拷贝之间的差距主要为一点，修改拷贝目标对象的内容是否影响拷贝源对象。

浅拷贝的实现:

源对象和目标对象:

    var target = {},        data = {            undefined: undefined,            empty: null,            empty_string: '',            number: 1,            string: 'test',            boolean: true,            object: {                number: 2            },            array: ['a', 'b'],            fun: function () {                console.log('test');            },            data: data        };

一、for-in循环

    for (var key in data) {        target[key] = data[key];    }    target.number = 2;    console.log(data.number);  //1    target.string = 'copy';    console.log(data.string);  //test    target.object.number = 5;      console.log(data.object.number); //5    target.array.push('c');  //["a", "b", "c"]    console.log(data.array);    target.fun = function () {        console.log('copy');      }    data.fun(); //test

二、Object.assign

    target = Object.assign({},data);    target.number = 2;    console.log(data.number);  //1    target.string = 'copy';    console.log(data.string);  //test    target.object.number = 5;      console.log(data.object.number); //5    target.array.push('c');  //["a", "b", "c"]    console.log(data.array);    target.fun = function () {        console.log('copy');      }    data.fun(); //test

可以看出target修改对象中的值类型,data中相对应的值未发生变化，但是修改了对象中的引用类型，data中相对象的值发生了变化。这是因为for-in循环和Object.assign仅复制了源对象最外层的属性，对于内层的对象仅复制了一份引用，所以修改了目标对象会影响源对象。

深拷贝实现

一、递归for-in循环

    function deepCopy(tar, resource) {            for (var key in resource) {                var source = resource[key];                if (Object.prototype.toString.call(source) === '[object Object]') {                    tar[key] = deepCopy(tar[key] || {}, resource[key]);                } else if(Object.prototype.toString.call(source) === '[object Array]'){                    tar[key] = deepCopy(tar[key] || [], resource[key]);                } else if(resource.hasOwnProperty(key)){                    tar[key] = resource[key];                }            }            return tar;        }        target = deepCopy(target, data);        target.number = 2;        console.log(data.number); //1        target.string = 'copy';        console.log(data.string);  //test        target.object.number = 5;        console.log(data.object.number);  //2        target.array.push('c');        console.log(data.array);  //["a", "b"]        target.fun = function () {            console.log('copy');        }        data.fun();        console.log(target); //test

二、JSON.parse和JSON.stringify

        target = JSON.parse(JSON.stringify(data));        target.number = 2;        console.log(data.number);  //1        target.string = 'copy';        console.log(data.string);  //test        target.object.number = 5;        console.log(data.object.number);  //2        target.array.push('c');        console.log(data.array);  //["a", "b"]

可以看出深拷贝不会出现修改目标对象影响源对象的问题，但使用JSON.parse和JSON.stringify方法进行深拷贝将无法拷贝JSON不支持的类型（如function，undefined等）。

over…