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JS实现DeepCopy的两种方式
1、寻常递归
var deepCopy = function(o) {
if (o instanceof Array) { //先判断Array
var n = [];
for (var i = 0; i < o.length; ++i) {
n[i] = deepCopy(o[i]);
}
return n;
} else if (o instanceof Object) {
var n = {}
for (var i in o) {
n[i] = deepCopy(o[i]);
}
return n;
} else {
return o;
}
}
2、Vuex源码中使用的方法
/**
* Get the first item that pass the test
* by second argument function
*
* @param {Array} list
* @param {Function} f
* @return {*}
*/
function find (list, f) {
return list.filter(f)[0]
}
/**
* Deep copy the given object considering circular structure.
* This function caches all nested objects and its copies.
* If it detects circular structure, use cached copy to avoid infinite loop.
*
* @param {*} obj
* @param {Array<Object>} cache
* @return {*}
*/
function deepCopy (obj, cache) {
if ( cache === void 0 ) cache = [];
// just return if obj is immutable value
if (obj === null || typeof obj !== 'object') {
return obj
}
// if obj is hit, it is in circular structure
var hit = find(cache, function (c) { return c.original === obj; });
if (hit) {
return hit.copy
}
var copy = Array.isArray(obj) ? [] : {};
// put the copy into cache at first
// because we want to refer it in recursive deepCopy
cache.push({
original: obj,
copy: copy
});
Object.keys(obj).forEach(function (key) {
copy[key] = deepCopy(obj[key], cache);
});
return copy
}
/**
* forEach for object
*/
// Credits: borrowed code from fcomb/redux-logger
为什么需要DeepCopy
在JS里,除Array和Object之外的数据类型的复制可以直接通过等号=来实现,但Array和Object类型的数据通过等号只是起引用作用,指向的是同一块内存地址。当源数据改变,引用的数据也同时会发生变化。