1.封装一个forEach方法
function forEach(arr,fn){
for(var i =0 ;i<arr.length; i++){
fn(arr[i],i,arr)
}
}
// 调用
forEach([1,2,3],function(item,index){
console.log("index:",index,"item:",item)
})
2.封装一个map方法
function map(arr,fn){
var newArray =[]
for(var i =0;i<arr.length;i++){
newArray.push(fn(arr[i],i,arr))
}
return newArray
}
var a =map([1,2,3],(item)=>item)
console.log(a) //[1,2,3]
3.封装一个every方法
function every(arr,fn){
var is = true
for(var i = 0; i < arr.length; i++){
if(!fn(arr[i],i,arr)){
is = false
}
}
return is
}
4.封装一个some方法
function some(arr,fn){
var is = false
for(var i = 0; i < arr.length; i++){
if(fn(arr[i],i,arr)){
is = true
}else{
is = false
}
}
return is
}
