使用javascript计算速度 [英] Calculate speed using javascript

问题描述

在下面的代码中，我试图计算图像的下载速度，但速度是无穷大。我究竟做错了什么？

In the code below, I am trying to calculate the download speed of an image, but the speed comes out as infinity. What am I doing wrong?

var imageAddr = "/images/image.jpg" + "?n=" + Math.random();
var startTime, endTime;
var downloadSize = 200000;
var download = new Image();
download.onload = function () {
    endTime = (new Date()).getTime();
    showResults();
}
startTime = (new Date()).getTime();
download.src = imageAddr;

function showResults() {
    var duration = Math.round((endTime - startTime) / 1000);
    var bitsLoaded = downloadSize * 8;
    var speedBps = Math.round(bitsLoaded / duration);
    var speedKbps = (speedBps / 1024).toFixed(2);
    var speedMbps = (speedKbps / 1024).toFixed(2);
    alert("Your connection speed is: \n" + 
           speedBps + " bps\n"   + 
           speedKbps + " kbps\n" + 
           speedMbps + " Mbps\n" );
}

推荐答案

试想一下： endTime 和 startTime 在 [ms] 中，所以他们的区别也是在ms。

Just think about it: endTime and startTime are in [ms], so their difference is also in ms.

300毫秒的图像加载示例：

Math.round((endTime - startTime) / 1000);
-> Math.round(300 / 1000);
-> Math.round(0.3);
-> 0

离开 Math.round 片段。

然后其他人声明持续时间= 0 将导致

speedBps = bitsLoaded / duration
-> speedBps = bitsLoaded / 0
-> speedBps = Infinity

但，请注意您无法准确结果是这样的。有延迟，连接时间，到第一个字节的时间等，无法衡量通过您的示例，以及图像< 1 MB 会导致非常不准确的结果。

But, please note that you can't get accurate results like this. There is latency, connection time, time to first byte, etc which cannot be measured by your example, and for an image < 1 MB they will lead to very inaccurate results.

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