深拷贝target为数组或者对象

cloneTarget(target, map = new WeakMap()) {
        if (typeof target === 'object') {
            const isArray = Array.isArray(target);
            let cloneTarget = isArray ? [] : {};
            if (map.get(target)) {
                return map.get(target);
            }
            map.set(target, cloneTarget);
            const keys = isArray ? undefined : Object.keys(target);
            this.forEach(keys || target, (value, key) => {
                if (keys) {
                    key = value;
                }
                cloneTarget[key] = this.cloneTarget(target[key], map);
            });
            return cloneTarget;
        } else {
            return target;
        }
    },
    //深复制遍历方法用到
    forEach(array, iteratee) {
        let index = -1;
        const length = array.length;
        while (++index < length) {
            iteratee(array[index], index);
        }
        return array;
    },