JavaScript中For循环和Map循环耗时比较

先看函数代码：

(function () {
    let utcTimeArray = [];
    let utcDateArrayAll = [];
    let utcDateArray = [2017/09/18 23:59:00, 2017/09/17 23:00:00, 2017/09/16 22:20:00, 2017/09/15 22:11:00, 2017/09/14 22:44:00, 2017/09/13 22:30:00, 2017/09/12 23:10:00];
    let time1 = new Date().getTime();
    for (let count = 0; count < 10000; count ++) {
        utcDateArrayAll = utcDateArrayAll.concat(utcDateArray);
    }
    let time2 = new Date().getTime();
    for (let date of utcDateArrayAll) {
        utcTimeArray.push(new Date(date).getTime());
    }
    let time3 = new Date().getTime();
    utcDateArrayAll.map((date) => {
        utcTimeArray.push(new Date(date).getTime());
    });
    let time4 = new Date().getTime();
    console.log("length: " + utcDateArrayAll.length);
    console.log("Concat Array lost time: " + (time2 - time1));
    console.log("For lost time: " + (time3 - time2));
    console.log("Map lost time: " + (time4 - time3));
})();

length: 70000
Concat Array lost time: 1634
For lost time: 42
Map lost time: 50

JavaScript函数中，如果数据量比较大，比如说上万的数据，For of循环速度更快，只有Map耗时的80%左右，故在大数据遍历的时候，建议使用For循环遍历。