apply原理源码实现

   Function.prototype.myApply = function (context) {
            var context = context || window
            context.fn = this
            var args = [...arguments].slice(1)
            if (!args) {
                var result = context.fn()
            } else {
                var result = context.fn(...args[0])
            }
            delete context.fn
            return result

        }
        function People(name,age){
            this.name=name
            this.age=age
            this.sayName=function(){
                console.log(arguments)
                console.log(this.name+'  '+this.age)
            }
        }
        function Stu(name,age){
            this.name=name
            this.age=age
        }
        var obj={
            name:'xiaozhang',
            age:1,
            sayName:function(name,age){
                
                this.name=name
                this.age=age
                 console.log(this.name+'  '+this.age)
                
            }
        }
        var stu=new Stu("tom1",18)
        var people=new People("mary",20)
        people.sayName.myApply(stu,["jerry",14])