call & apply实现

let a = {
    y:'zjy',
    x(m,n){
        console.log(this.y,m,n)
    }
}
let b = {
    y:'lyn'
}
a.x.call(b,1,2) //lyn 1 2
a.x.apply(b,[1,2]) //lyn 1 2

call

Function.prototype.myCall = function(obj,...args){
　　obj = obj ? Object(obj) : window
　　obj.fn = this
　　let res = obj.fn(...args)//隐式绑定
　　delete obj.fn
　　return res
}

apply

Function.prototype.myApply = function(obj,args){
　　obj = obj ? Object(obj) : window
　　obj.fn = this
　　let res = obj.fn(...args)//隐式绑定
　　delete obj.fn
　　return res
}

注：为什么参数的第一个值不默认设置为window，防止实参为null，undefined