foo.Mycall(obj,1,2,3)
Function.prototype.Mycall=function(target,...args){
    if(typeof this!=='function'){
        throw new TypeError('this is not a function')
    }
    // 判断target是否是对象
    if(target==null||target==undefined){
        target=window
    }
    if(typeof target!=='object'){
        target=Object(target)
    }
    // 把this作为target的方法
    let key=new Symbol()
    target[key]=this;

    let res=target[key](...args)
    delete target[key]
    return res
}

apply和call差不多，都是直接返回函数执行的结果

区别：apply传入的参数是数组

foo.Myapply(obj,[1,2,3])

Function.prototype.Myapply=function(target,args){
    if(typeof this!=='function'){
        throw new TypeError('this is not a function')
    } 
    if(target==null||target===undefined){
        target=window
    }
    if(typeof target!=='object'){
        target=Object(target)
    }

    let key=new Symbol()
    target[key]=this;

    let res=target[key](...args)
    delete target[key]
    return res
}

bind:

Function.prototype.bind=function(context,...args){
    if(typeof this!=='function'){
        throw new Error('this is not a function')
    }
    if(context==null||context==undefined){
        context=window
    }
    if(context!=='object'){
        context=Object(context)
    }
    let key=new Symbol()
    context[key]=this;
    return function(...newargs){
        let res=context[key](...args,...newargs)
        delete context[key]
        return res
    }
}