TypeScript判断对象类型的四种方式

一、typeof

typeof "";  //stringtypeof 1;   //numbertypeof false; //booleantypeof undefined; //undefinedtypeof function(){}; //functiontypeof {}; //objecttypeof Symbol(); //symboltypeof null; //objecttypeof []; //objecttypeof new Date(); //objecttypeof new RegExp(); //object

二、instanceof

{} instanceof Object; //true[] instanceof Array;  //true[] instanceof Object; //true"123" instanceof String; //falsenew String(123) instanceof String; //true

三、constructor

function instance(left,right){    let prototype = right.prototype;  //获取类型的原型    let proto = left.__proto__;       //获取对象的原型    while(true){    //循环判断对象的原型是否等于类型的原型，直到对象原型为null，因为原型链最终为null       if (proto === null || proto === undefined){           return false;       }       if (proto === prototype){           return true;       }       proto = proto.__proto__;     }}console.log(instance({},Object)); //trueconsole.log(instance([],Number)); //false

四、Object.prototype.toString()

function getType(obj){  let type  = typeof obj;  if(type != "object"){    return type;  }  return Object.prototype.toString.call(obj).replace(/^\[object (\S+)\]$/, '');}

使���案例：

const vFocus = {  mounted: (el: HTMLElement, binding: any) => {    // 指令绑定的元素    console.log(typeof el);    console.log(el);    // 指令绑定的参数    console.log(binding)    // 如果是输入框    if (el instanceof HTMLInputElement) {      // 元素聚焦      el.focus();      el.placeholder = '请输入';      el.value = '勤奋、努力'    }else if (el instanceof HTMLAnchorElement) {      // 如果是标签我们就导向 百度翻译      el.href='https://fanyi.baidu.com/'    }  }}      百度一下，你就知道