JS底层手写

instanceOf

        function myInstanceof(left, right) {
     
            //基本数据类型直接返回false 
            if(typeof left !== 'object' || left === null) return false; 
            //getProtypeOf是Object对象自带的一个方法，能够拿到参数的原型对象 
            let proto = Object.getPrototypeOf(left); 
            while(true) {
     
                //查找到尽头，还没找到 
                if(proto == null) return false; 
                //找到相同的原型对象 
                if(proto == right.prototype) return true; 
                proto = Object.getPrototypeOf(proto); 
            } }

防抖

        var btn=document.querySelector('button')
        var ipt=document.querySelector('input')
        btn.addEventListener('click',debounce(getValue,2000))
        function getValue(){
    
            var val=ipt.value
            console.log(val);
        }
        function debounce(fn,time){
    
            let t=null
            return function(){
    
                if(t){
    
                    clearTimeout(t)
                }
                var firstClick=!t
                if(firstClick){
    
                    fn.apply(this,arguments)
                }
                t=setTimeout(() => {
    
                    t=null
                }, time);
            }
        }

节流

        var btn=document.querySelector('button')
        var ipt=document.querySelector('input')
        btn.addEventListener('click',throttle(getValue,2000))
        function getValue(){
    
            var val=ipt.value
            console.log(val);
        }
        function throttle(fn,time){
    
            var begin=0
            return function(){
    
                var date=new Date().getTime()
                if(date-begin>time){
    
                    fn.apply(this,arguments)
                    begin=date
                }
            }
        }

call

        Function.prototype.myCall = function (obj) {
    
                var obj = obj || window
                obj.fn = this//指向person
                var args = [...arguments].slice(1)
                var result = obj.fn(...args)
                // 删除 fn
                delete obj.fn
                return result
            }
            function person(a,b,c){
    
                return {
    
                    name:this.name,
                    a:a,b:b,c:c
                }
            }
            var obj={
    
                name:'jack'
            }
            var bili=person.myCall(obj,1,2,3)
            console.log(bili);

apply

        Function.prototype.myApply = function (context,arr) {
    
                var context = context || window
                context.fn = this
                // 需要判断是否存储第二个参数
                // 如果存在，就将第二个参数展开
                if (arr) {
    
                    result= context.fn(...arr)
                } else {
    
                    result = context.fn()
                }

                delete context.fn
                return result
            }
            function person(a, b, c) {
    
                    return {
    
                        name: this.name,
                        a: a, b: b, c: c
                    }
                }
            var obj = {
    
                name: 'jack'
            }
            console.log(person.myApply(obj,[1,2,3]));

bind