数组方法源码

map

Array.prototype.myMap=function(f){
    let a=[];
    for (let i=0;i<this.length;i++){
        a.push(f(this[i]))
    }
    return a;
}

  Array.prototype.myMap=function(){
            if(arguments.length==1&& typeof arguments[0]=="function"){ 
                var newarr=[];
                for(var i=0;i<this.length;i++){
                    arguments[0].call(window,this[i],i,this);
                    var new_num=arguments[0](this[i],i,this);
                    newarr.push(new_num);
                }
            }
            return newarr
        }

reduce

Array.prototype.myReduce=function (f,value=0) {
    for (let i =0 ;i<this.length;i++){
        value=f(this[i],value)
    }
    return value
}

filter

Array.prototype.myFilter=function (f,value=0) {
    let a=[]
    for (let i =0 ;i<this.length;i++){
        let flag=f(this[i],value)
        if (flag) a.push(this[i])
    }
    return a
}

  Array.prototype.myFilter=function(){
            if(arguments.length==1&&typeof arguments[0]=="function"){
                var newarr=[];
                for(var i=0;i<this.length;i++){
                    arguments[0].call(window,this[i],i,this);
                    var flag=arguments[0](this[i],i,this);
                    if(flag){
                        newarr.push(this[i]);
                    }
                }
            }
            return newarr;
        }

foreach

Array.prototype.myForEach=function (f) {
    for (let i=0;i<this.length;i++){
        f(this[i])
    }
}
     Array.prototype.myForEach=function(){
            if(arguments.length==1&&typeof arguments[0]=="function"){
                for(var i=0;i<this.length;i++){
                    arguments[0].call(window,this[i],i,this)
                }
            }else if(arguments.length==2){
                for(var i=0;i<this.length;i++){
                    arguments[0].call(arguments[1],this[i],i,this);
                }
            }
        }

some

Array.prototype.mySome=function (f) {
    let flag=false;
    for (let i=0;i<this.length;i++){
        flag =f(this[i])
        if (flag) return flag
    }
    return flag;
}
     Array.prototype.mySome=function(){
            if(arguments.length==1&&typeof arguments[0]=="function"){
                for(var i=0;i<this.length;i++){
                    arguments[0].call(window,this[i],i,this);
                    var flag=arguments[0](this[i],i,this)
                    if(flag){
                        return flag;
                    }
                }
            } 
            return false;
        }

every

Array.prototype.myEvery=function (f) {
    let flag=true
    for (let i=0;i<this.length;i++){
        flag =f(this[i])
        if (!flag) return flag
    }
    return flag
}

 Array.prototype.myEvery=function(){
            var flag=true;
            if(arguments.length==1&&typeof arguments[0]=="function"){
                for(var i=0;i<this.length;i++){
                    arguments[0].call(window,this[i],i,this)
                    flag=arguments[0](this[i],i,this)
                    if(!flag){
                        return flag;
                    }
                }
            }
            return flag;
        }