1.浅拷贝

// 浅拷贝
let shallowCopy = function (obj) {
    if (typeof obj !== 'object') return
    let newObj = obj instanceof Array ? [] : {}
    for (let key in obj) {
        if (obj.hasOwnProperty(key)) {
            newObj[key] = obj[key]
        }
    }
    return newObj
}

2.深拷贝

// 递归深拷贝
let deepCopy = function (obj) {
    if (typeof obj !== 'object') return
    let newObj = obj instanceof Array ? [] : {}
    for (var key in obj) {
        if (obj.hasOwnProperty(key)) {
            newObj[key] = typeof obj[key] === 'object' ? deepCopy(obj[key]) : obj[key];
        }
    }
    return newObj
}

// 入栈深拷贝
let cloneDeep = function (obj) {
    let root = Array.isArray(obj) ? [] : {};
    let stack = [{
        parent: root,
        key: undefined,
        data: obj
    }]
    while (stack.length) {
        let node = stack.pop()
        let parent = node.parent
        let key = node.key
        let data = node.data
        // 初始化赋值目标，key为undefined则拷贝到父元素，否则拷贝到子元素
        let res = parent;
        if (typeof key !== 'undefined') {
            res = parent[key] = Array.isArray(data)? [] : {};
        }
        for (let k in data) {
            if(data.hasOwnProperty(k)) {
                if (typeof data[k] === 'object') {
                    stack.push({parent: res, key: k, data: data[k]})
                } else {
                    res[k] = data[k];
                }
            }
        }
    }
    return root
}