Example analysis of iteration method of Array array in javascript_javascript skills

num.filter(function(item, index, array){
return (item > 2); //[3, 4, 5, 6, 12]
});

//map() returns an array, each item in the array is the result of running the passed parameters on the corresponding item in the original array

var num = [1,2,3,4,5,4,3,2,1];
num.map(function(item, index, array){
return (item * 2); //[2, 4, 6, 8, 10, 8, 6, 4, 2]
});

//every() some(), query whether an item in the array meets a certain condition. Every() must pass in every parameter to return true, and the result will be true; some() method
//As long as one of them is true, the result is true

var num = [1,2,3,4,5,4,3,2,1];
num.every(function(item, index, array){
return (item > 2); //false
});

num.some(function(item, index, array){
return (item > 2); //true
})

//forEach() passes parameters to each item in the array and has no return value
var num = [1,2,3,4,5,4,3,2,1];
num.forEach(function(item, index, array){
return item;
})