deep Copy

deepCopy.js

/*
    Object.getPrototypeOf
    Object.setPrototypeOf
    也可以用来处理 原型相关的事物
*/

function deepCopy(obj, m = new WeakMap()){
    let type = Object.prototype.toString.call(obj)
    if (m.has(obj)) { return m.get(obj) }
    switch (type) {
        case '[object Null]':
        case '[object Undefined]':
        case '[object Number]':
        case '[object String]':
        case '[object Function]':
        case '[object Symbol]':
            return obj
        case '[object Date]':
            return new Date(obj)
        case '[object RegExp]':
            return new RegExp(obj)
        case '[object Array]':
            {
                let ret = []
                m.set(obj, ret)
                for (let key in obj) {
                    if (obj.hasOwnProperty(key)) {
                        ret[key] = deepCopy(obj[key], m)
                    }
                }
                return ret
            }
        case '[object Object]':
            {
                let ret = {}
                let isPlainObj = function(obj) {
                    const proto = Object.getPrototypeOf(obj)
                    return proto === Object.prototype || proto === null
                }
                if (!isPlainObj(obj)) {
                    ret = Object.create(obj.constructor.prototype)
                    /* 
                        Object.create is undefined
                        let F = function() {}
                        F.prototype = obj.constructor.prototype
                        ret = new F() 
                        
                        OR
                        
                        Object.setPrototypeOf(ret, obj.constructor.prototype)
                    */
                }
                m.set(obj, ret)
                for (let key in obj) {
                    if (obj.hasOwnProperty(key)) {
                        ret[key] = deepCopy(obj[key], m)
                    }
                }
                return ret
            }

        default:
            return obj
    }
}