浅拷贝与深拷贝
浅拷贝 是创立一个新对象,这个对象有着原始对象属性值的拷贝。如果属性是根本类型,拷贝的就是根本类型的值,如果属性是援用类型,拷贝的是内存地址。如果不进行深拷贝,其中一个对象扭转了对象的值,就会影响到另一个对象的值。
深拷贝 是将一个对象从内存中残缺的拷贝一份进去, 从堆内存中开拓一个新的区域寄存新对象, 且批改新对象不会影响原对象。
1.JSON.parse(JSON.stringify(obj))
个别状况下对一般对象须要进行深拷贝,能够应用这种办法进行深拷贝操作,这种是最简略且代码量起码的深拷贝办法。
let a = {a:1,b:2}
let b = JSON.parse(JSON.stringify(a))
a.a = 11
console.log(a)//{a:1,b:2}
console.log(b)//{a:11,b:2}
1.1 JSON.parse(JSON.stringify(obj))深浅拷贝的缺点
let a = {
name: 'Jack',
age: 18,
hobbit: ['sing', {type: 'sports', value: 'run'}],
score: {math: 'A',},
run: function() {},
walk: undefined,
fly: NaN,
cy: null,
date: new Date()}
let b = JSON.parse(JSON.stringify(a))
console.log(b)
// {
// age: 18,
// cy: null,
// date: "2022-05-15T08:04:06.808Z"
// fly: null,
// hobbit: (3) ["dance", "sing", {…}],
// name: "Jack",
// score: {math: "A"},
// }
取不到值为 undefined 的 key;如果对象里有函数,函数无奈被拷贝下来;无奈拷贝 copyObj 对象原型链上的属性和办法;对象转变为 date 字符串。
2. 一般递归函数实现深拷贝
function deepClone(source) {if (typeof source !== 'object' || source == null) {return source;}
const target = Array.isArray(source) ? [] : {};
for (const key in source) {if (Object.prototype.hasOwnProperty.call(source, key)) {if (typeof source[key] === 'object' && source[key] !== null) {target[key] = deepClone(source[key]);
} else {target[key] = source[key];
}
}
}
return target;
}
2.1 解决循环援用和 symblo 类型
function cloneDeep(source, hash = new WeakMap()) {if (typeof source !== 'object' || source === null) {return source;}
if (hash.has(source)) {return hash.get(source);
}
const target = Array.isArray(source) ? [] : {};
Reflect.ownKeys(source).forEach(key => {const val = source[key];
if (typeof val === 'object' && val != null) {target[key] = cloneDeep(val, hash);
} else {target[key] = val;
}
})
return target;
}
3. 兼容多种数据类型
const deepClone = (source, cache) => {if(!cache){cache = new Map()
}
if(source instanceof Object) { // 不思考跨 iframe
if(cache.get(source)) {return cache.get(source) }
let result
if(source instanceof Function) {if(source.prototype) { // 有 prototype 就是一般函数
result = function(){ return source.apply(this, arguments) }
} else {result = (...args) => {return source.call(undefined, ...args) }
}
} else if(source instanceof Array) {result = []
} else if(source instanceof Date) {result = new Date(source - 0)
} else if(source instanceof RegExp) {result = new RegExp(source.source, source.flags)
} else {result = {}
}
cache.set(source, result)
for(let key in source) {if(source.hasOwnProperty(key)){result[key] = deepClone(source[key], cache)
}
}
return result
} else {return source}
}
4.jQuery.extend()办法
能够应用 $.extend 进行深拷贝
$.extend(deepCopy, target, object1, [objectN])// 第一个参数为 true, 就是深拷贝
let a = {
a: 1,
b: {d:8},
c: [1, 2, 3]
};
let b = $.extend(true, {}, a);
console.log(a.b.d === b.b.d); // false
4.1 jQuery.extend 源码
jQuery.extend = jQuery.fn.extend = function() {
var options,
name,
src,
copy,
copyIsArray,
clone,
target = arguments[0] || {},
i = 1,
length = arguments.length,
deep = false;
// Handle a deep copy situation
if (typeof target === "boolean") {
deep = target;
// Skip the boolean and the target
target = arguments[i] || {};
i++;
}
// Handle case when target is a string or something (possible in deep copy)
if (typeof target !== "object" && !jQuery.isFunction(target)) {target = {};
}
// Extend jQuery itself if only one argument is passed
if (i === length) {
target = this;
i--;
}
for (; i < length; i++) {
// Only deal with non-null/undefined values
if ((options = arguments[i]) != null) {
// Extend the base object
for (name in options) {src = target[name];
copy = options[name];
// Prevent never-ending loop
if (target === copy) {continue;}
// Recurse if we're merging plain objects or arrays
if (
deep &&
copy &&
(jQuery.isPlainObject(copy) || (copyIsArray = Array.isArray(copy)))
) {if (copyIsArray) {
copyIsArray = false;
clone = src && Array.isArray(src) ? src : [];} else {clone = src && jQuery.isPlainObject(src) ? src : {};}
// Never move original objects, clone them
target[name] = jQuery.extend(deep, clone, copy);
// Don't bring in undefined values
} else if (copy !== undefined) {target[name] = copy;
}
}
}
}
// Return the modified object
return target;
};