js迭代方法every(),filter(),forEach(),map()和some()实例讲解

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

    alert(everyResult);//fasle

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

    alert(someResult);//true

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

    alert(filterResult);//3,4,5,4,3

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

    alert(mapResult);//2,4,6,8,10,8,6,4,2

    //forEach
    num.forEach(function (item, index, array) {
        //执行想要执行的操作
    });