判断值的类型并返回

const valType = (target) => {
    const template = {
      "[object Array]":"array",
      "[object Object]":"object",
      "[object Number]":"number",
      "[object Boolean]":"boolean",
      "[object String]":"string"
    }
    if(!target) return 'null';
    const t = Object.prototype.toString.call(target);
    return template[t];
}