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学些js call apply bind的新的收获,做个记录,希望大家多多指导

 call: 改变当前执行上下文的this指针

function dog(color){     this.color = color;}dog.prototype.eat = function(){  return   this.color+ " dog can eat food";}var blackDog = new dog(‘black‘);blackDog.eat();// black dog can eat foodvar redDog = {  color: "red"      }blackDog.eat.call(redDog);//red dog can eat food

总结: 一开始blackDog 对象中的this只向其本身,所以this.color就是实例化对象时传入的black, 然而当执行blackDog.eat.call(redDog)这个方法时,通过call方法改变了this的指向,this 指向redDog, 所以this.color就是red。

 

apply: 和call方法大致相同,改变当前执行上下文的this指针,但是传入的参数(第一个以外)是一个数组。

function dog(color){     this.color = color;}dog.prototype.showSkills= function(eat, run, jump){    console.log(this.color + " dog skill: " + eat +"," +  run +","+ jump);}var blackDog = new dog(‘black‘);var redDog = {  color: "red"}blackDog.showSkills.call(redDog, "eat", "run", "jump");//red dog skill: eat,run,jumpblackDog.showSkills.apply(redDog, ["eat", "run", "jump"]);//red dog skill: eat,run,jump

总结: 由此可见,call和apply用法大致相同,但是apply的在调用另一个方法是,传入的多个参数是数据,数组内的多个参数会以原有的顺序对应到每一接受器上。

 

bind: 功能与call和apply相似 其作用是改变某个方法的this指针,并且在该方法被调用时才会生效,而不像call和apply会理解执行

eg1:function bindDemo(){  console.log(this.a)  };bindDemo.bind({a: "i am this.a"}) //此处并没有被掉用,只是一个声明bindDemo.bind({a: "i am this.a"})();// i am this.aeg2:function cat(){    this.eat = function(){        console.log(this.name + " cat is eating");        } }var Cat = new cat();Cat.eat.call({name: "blackCat"});// blackCat cat is eatingCat.eat.apply({name: "redCat"});// redCat cat is eatingCat.eat.bind({name: "otherCat"}); //此处只会返回一个对象,不会有输出,因为还没有真正调用Cat.eat.bind({name: "otherCat"})();//otherCat cat is eating

总结: bind方法再被使用时,必须进行掉用才会执行,而call 和apply 则会直接掉用原来的方法,并改变this指针。

 

学些js call apply bind的新的收获,做个记录,希望大家多多指导