deep copy a object

deepCopy.js

/*
 * https://gist.github.com/yantze/c428dd022c0c85db2d14c37da4c1dec0
 * https://github.com/pvorb/clone/blob/master/clone.js#L74:8
 * author: yantze

 * typeoof
 * 对象为 function ,可能是 Function, class, Symbol, 不复制，因为这些是非结构化对象，但可以生成实例
 * 对象为 object, 可能是 Date 实例, class 实例，{}, [], Regex 实例, Buffer 实例, 错误实例
*/

function deepCopy(obj) {
    let map = new WeakMap()
    function __objToStr(o) {
        return Object.prototype.toString(o)
    }

    function _clone(obj) {
        if (obj === null || obj === undefined || typeof obj === 'function') {
            return obj
        }

        let existobj = map.get(obj)
        //如果这个对象已经被记录则直接返回
        if(existobj) {
            return existobj
        }

        let child
        let proto

        if (typeof obj === 'object' && Array.isArray(obj)) {
            child = []
        }
        if (typeof obj === 'object' && __objToStr(obj) === '[object RegExp]') {
            child = new RegExp(obj.source) // 缺少 flags
            return child
        }
        if (typeof obj === 'object' && __objToStr(obj) === '[object Date]') {
            child = new Date(obj)
            return child
        }
        if (typeof obj === 'object' && __objToStr(obj) === '[object Number]') {
            child = new Number(obj)
            return child
        }
        if (typeof obj === 'object' && __objToStr(obj) === '[object Boolean]') {
            child = new Boolean(obj)
            return child
        }
        if (typeof obj === 'object' && __objToStr(obj) === '[object String]') {
            child = new String(obj)
            return child
        }
        if (typeof obj === 'object' && __objToStr(obj) === '[object Symbol]') {
            child = new Symbol(obj)
            return child
        }
        if (typeof obj === 'object' && typeof Buffer !== 'undefined' && Buffer.isBuffer(a)) { // nodejs
            child = new Buffer(obj)
            return child
        }

        if (typeof obj === 'string') {
            return obj
        }
        if (typeof obj === 'number') {
            return obj
        }
        // Uint8Array, Uint16Array, Uint32Array, BufferArray
        if (child === undefined) {
            proto = Object.getPrototypeOf(obj)
            child = Object.create(proto)
        }

        map.set(obj, child)
        for (let i in obj) {
            // if (proto) {
            //     let attr = Object.getPrototypeOf(obj, i)
            //     if (attr && attr.set == null) continue
            // }

            child[i] = _clone(obj[i])
        }

        return child
    }

    return _clone(obj)
}