js數(shù)組遍歷性能比較問題

閑來無聊想看看數(shù)組各個遍歷的方法性能如何
不跑不知道一跑嚇一跳

var nativeMap = function (arr, callback) {
    return arr.map(callback);
};
var customMap = function (arr, callback) {
    var ret = [];
    for (var i = 0; i < arr.length; i++) {
        ret.push(callback(arr[i], i, arr));
    }
    return ret;
};

var forMap = function (arr, callback) {
    var ret = [];
    for(let elem of arr){
        ret.push(callback(elem))
    }
    return ret;
};

var run = function (name, times, fn, arr, callback) {
    // var start = (new Date()).getTime();
    console.time('遍歷時長');
    let newArr;
    for (var i = 0; i < times; i++) {
        newArr = fn(arr, callback);
    }
    console.log(name);
    console.timeEnd('遍歷時長');
};

var callback = function (item) {
    return item+'qwe';
};
let testArr = ['b','c','d','e','f','d','e','f','d','e','f','d','e','f','d','e','f','d','e','f'];
let length = testArr.length;
run('map遍歷', length, nativeMap, testArr, callback);
run('for循環(huán)', length, customMap, testArr, callback);
run('for-of循環(huán)', length, forMap, testArr, callback);

map遍歷
遍歷時長: 1.491ms
for循環(huán)
遍歷時長: 0.249ms
for-of循環(huán)
遍歷時長: 0.268ms

map遍歷比for循環(huán)慢我也忍了。為啥es6定義的for-of循環(huán)比for循環(huán)還慢。
讓我很費解