JS手写call,apply,bind

1.手写call,apply,bind

//call
Function.prototype.myCall = function(context){
    context = context || window
    context.fn = this
    let arg = [...arguments].slice(1)
    let result = context.fn(...arg)
    delete context.fn
    return result
}

//apply
Function.prototype.myApply = function(context){
    context = context || window
    context.fn = this
    let result
    //这里判断如果有第二个参数，就是一个数组
    if(arguments[1]){
        result = context.fn(...arguments[1])
    }else{
        result = context.fn()
    }
    delete context.fn
    return result
}

// bind
//考虑到原型链，因为在new 一个bind过生成的新函数的时候，必须的条件是要继承原函数的原型
Function.prototype.myBind = function(thisArg){
    if(typeof this !== 'function') return
    let that = this
    let arg = [...arguments].slice(1)
    let fnNop = function(){}
    let fn = function(){
        return that.apply(this instanceof fn ? this : thisArg , arg.concat([...arguments]))
    }
    // 维护原型关系
    if(this.prototype){
        fnNop.prototype = this.prototype
    }
    fn.prototype = new fnNop()
    return fn
}