Array.prototype._filter = function (fn){
if(typeof fn !== "function") return ;
let arr = [];
for(let i = 0;i<this.length;i++){
if(fn(this[i],i,this)){
arr.push(this[i])
}
}
return arr;
}
Array.prototype._filter = function (fn){
if(typeof fn !== "function") return ;
let arr = [];
for(let i = 0;i<this.length;i++){
if(fn(this[i],i,this)){
arr.push(this[i])
}
}
return arr;
}