As I outline in this other answer here on StackOverflow, you can do this by timing the download of files of various sizes (start small, ramp up if the connection seems to allow it), ensuring through cache headers and such that the file is really being read from the remote server and not being retrieved from cache. This doesn't necessarily require that you have a server of your own (the files could be coming from S3 or similar), but you will need somewhere to get the files from in order to test connection speed.

也就是说，时间点带宽测试是出了名的不可靠，因为它们会受到其他窗口中正在下载的其他项目、服务器的速度、路由中的链接等的影响。但是你可以用这种方法得到一个大致的概念。

As I outline in this other answer here on StackOverflow, you can do this by timing the download of files of various sizes (start small, ramp up if the connection seems to allow it), ensuring through cache headers and such that the file is really being read from the remote server and not being retrieved from cache. This doesn't necessarily require that you have a server of your own (the files could be coming from S3 or similar), but you will need somewhere to get the files from in order to test connection speed.

也就是说，时间点带宽测试是出了名的不可靠，因为它们会受到其他窗口中正在下载的其他项目、服务器的速度、路由中的链接等的影响。但是你可以用这种方法得到一个大致的概念。

图像技巧很酷，但在我的测试中，它是在我想完成的一些ajax调用之前加载的。

2017年合适的解决方案是使用工人(http://caniuse.com/#feat=webworkers)。

工人看起来像这样:

/**
 * This function performs a synchronous request
 * and returns an object contain informations about the download
 * time and size
 */
function measure(filename) {
  var xhr = new XMLHttpRequest();
  var measure = {};
  xhr.open("GET", filename + '?' + (new Date()).getTime(), false);
  measure.start = (new Date()).getTime();
  xhr.send(null);
  measure.end = (new Date()).getTime();
  measure.len = parseInt(xhr.getResponseHeader('Content-Length') || 0);
  measure.delta = measure.end - measure.start;
  return measure;
}

/**
 * Requires that we pass a base url to the worker
 * The worker will measure the download time needed to get
 * a ~0KB and a 100KB.
 * It will return a string that serializes this informations as
 * pipe separated values
 */
onmessage = function(e) {
  measure0 = measure(e.data.base_url + '/test/0.bz2');
  measure100 = measure(e.data.base_url + '/test/100K.bz2');
  postMessage(
    measure0.delta + '|' +
    measure0.len + '|' +
    measure100.delta + '|' +
    measure100.len
  );
};

调用Worker的js文件:

var base_url = PORTAL_URL + '/++plone++experimental.bwtools';
if (typeof(Worker) === 'undefined') {
  return; // unsupported
}
w = new Worker(base_url + "/scripts/worker.js");
w.postMessage({
  base_url: base_url
});
w.onmessage = function(event) {
  if (event.data) {
    set_cookie(event.data);
  }
};

摘自我编写的Plone包的代码:

https://github.com/collective/experimental.bwtools/blob/master/src/experimental/bwtools/browser/static/scripts/

//JUST AN EXAMPLE, PLEASE USE YOUR OWN PICTURE! var imageAddr = "https://i.ibb.co/sPbbkkZ/pexels-lisa-1540258.jpg"; var downloadSize = 10500000; //bytes function ShowProgressMessage(msg) { if (console) { if (typeof msg == "string") { console.log(msg); } else { for (var i = 0; i < msg.length; i++) { console.log(msg[i]); } } } var oProgress = document.getElementById("progress"); if (oProgress) { var actualHTML = (typeof msg == "string") ? msg : msg.join("<br />"); oProgress.innerHTML = actualHTML; } } function InitiateSpeedDetection() { ShowProgressMessage("Loading the image, please wait..."); window.setTimeout(MeasureConnectionSpeed, 1); }; if (window.addEventListener) { window.addEventListener('load', InitiateSpeedDetection, false); } else if (window.attachEvent) { window.attachEvent('onload', InitiateSpeedDetection); } function MeasureConnectionSpeed() { var startTime, endTime; var download = new Image(); download.onload = function () { endTime = (new Date()).getTime(); showResults(); } download.onerror = function (err, msg) { ShowProgressMessage("Invalid image, or error downloading"); } startTime = (new Date()).getTime(); var cacheBuster = "?nnn=" + startTime; download.src = imageAddr + cacheBuster; function showResults() { var duration = (endTime - startTime) / 1000; var bitsLoaded = downloadSize * 8; var speedBps = (bitsLoaded / duration).toFixed(2); var speedKbps = (speedBps / 1024).toFixed(2); var speedMbps = (speedKbps / 1024).toFixed(2); ShowProgressMessage([ "Your connection speed is:", speedBps + " bps", speedKbps + " kbps", speedMbps + " Mbps" ]); } } <h1 id="progress">JavaScript is turned off, or your browser is realllllly slow</h1>

小片段:

var speedtest = {};
function speedTest_start(name) { speedtest[name]= +new Date(); }
function speedTest_stop(name) { return +new Date() - speedtest[name] + (delete 
speedtest[name]?0:0); }

使用:

speedTest_start("test1");

// ... some code

speedTest_stop("test1");
// returns the time duration in ms

还可以进行更多的测试:

speedTest_start("whole");

// ... some code

speedTest_start("part");

// ... some code

speedTest_stop("part");
// returns the time duration in ms of "part"

// ... some code

speedTest_stop("whole");
// returns the time duration in ms of "whole"

由于Punit S的回答，为了检测动态连接速度的变化，你可以使用以下代码:

navigator.connection.onchange = function () {
 //do what you need to do ,on speed change event
 console.log('Connection Speed Changed');
}