javascript面试基础

1、this call apply bind
一个例子理解 call apply bind 都是为了改变this指向的问题

  function sayHello(para){
        console.log(`${para} ${this.name}`)
      }

      person={
        name:'zdq'
      }
      sayHello.call(person,'hello','world')

      sayHello.apply(person,['hi'])

      const newSayHello= sayHello.bind(person)
      newSayHello('hh')

自定义call

 Function.prototype.myCall=function(context){
        const fn =this;
        context.fn=fn
        const args = Array.from(arguments).slice(1);
       const result= context.fn(...args)
       delete context.fn
       return result
      }
      sayHello.myCall(person,'自定义call')

//自定义实现一个apply

      Function.prototype.myApply=function(context,args){
      console.log('myApply',args)  
      const fn =this;
      context.fn=fn
      const result=context.fn(...args)
      delete context.fn
       return result
      }

 //手写bind函数
      Function.prototype.myBind=function(context){
        const fn=this;
        console.log('myBind',arguments)
        let args = Array.from(arguments).slice(1); //
        console.log('myBind',args)
        return function(){
            const newArr=args.concat(Array.from(arguments))
            fn.apply(context,newArr)
            console.log('myBind newArr',newArr)
            // fn.apply(context,args)
        }
      }
        // 声明一个函数
    function fn(a, b, c) {
        console.log("函数内部this指向:", this);
        console.log("参数列表:", a, b, c);
    }
    const newFun=fn.myBind({},10,20,30)
    newFun(40)