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…