手写apply-call-bind实现

call

 1 Function.prototype.myCall=function(thisArg,...args){
 2     let fn=this //隐式调用
 3     thisArg=(thisArg!==null&&thisArg!==undefined)?Object(thisArg):window //传undefined null 指向window全局
 4     thisArg.fn=fn //1
 5     let result=thisArg.fn(...args) //2
 6     delete thisArg.fn //3  1 2 3不用call调用
 7     return result //call函数有返回值
 8 }
 9 
10 function foo(){
11     console.log("foo调用了",this)
12 }
13 function sum(num1,num2){
14     return num1+num2
15 }
16 foo.myCall()
17 let re=sum.myCall({},20,30)
18 console.log(re)

apply

 1 Function.prototype.myApply=function(thisArg,argArray){
 2     let fn=this
 3     thisArg=(thisArg!==null&&thisArg!==undefined)?Object(thisArg):window
 4     thisArg.fn=fn
 5     let result
 6     //一:
 7     // if(!argArray){//没传值时
 8     //     result=thisArg.fn()
 9     // }else{//传值时
10     //     result=thisArg.fn(...argArray)
11     // }
12     //二:
13     // argArray=argArray?argArray:[]
14     //三:
15     argArray=argArray||[]
16     result=thisArg.fn(...argArray)
17     delete thisArg.fn
18     return result
19 }
20 
21 function foo(){
22     console.log("foo调用了",this)
23 }
24 function sum(num1,num2){
25     return num1+num2
26 }
27 foo.myApply({})
28 let re=sum.myApply({},[20,30])
29 console.log(re)

bind

 1 Function.prototype.myBind=function(thisArg,...argArray){
 2     //1.获取到真实需要调用的函数
 3     let fn=this
 4     //2.绑定this
 5     thisArg=(thisArg!==null&&thisArg!==undefined)?Object(thisArg):window
 6     function proxyFn(...arg){
 7         //3.将函数放到thisArg中进行调用
 8         thisArg.fn=fn
 9         //特殊：对两个传入的参数进行合并
10         let finalArg=[...argArray,...arg]
11         let result=thisArg.fn(...finalArg)
12         delete thisArg.fn
13         //4.返回结果
14         return result
15     }
16     return proxyFn
17 }
18 
19 function foo(){
20     console.log("foo执行了",this)
21 }
22 function sum(num1,num2, num3){
23     console.log(num1,num2,num3)
24     return num1+num2+num3
25 }
26 
27 let fn=foo.myBind({})
28 fn()
29 
30 let su=sum.myBind({},2,3)
31 let result=su(5)
32 console.log(result)