How Can I Measure Internet Speed Using JavaScript?

Detect Internet Speed with JavaScript

Many applications require the ability to measure the user's internet speed. While it's not always accurate, it can provide a helpful indication of the user's connectivity.

Approach

The solution involves loading an image with a known file size and calculating the speed based on the time taken to load it. This is done by:

1. Loading the image and setting an onload handler.
2. Measuring the start and end time of the image load using Date.getTime().
3. Computing the time taken to load the image in seconds.
4. Dividing the file size in bits by the time to obtain the speed in bits per second (bps).
5. Converting the speed to kilobits per second (kbps) and megabits per second (mbps) for better readability.

Example

The following code provides an implementation of this approach:

var imageAddr = "https://example.com/image.png";
var downloadSize = 7300000; //bytes

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; //seconds
    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:");
    ShowProgressMessage(speedBps + " bps");
    ShowProgressMessage(speedKbps + " kbps");
    ShowProgressMessage(speedMbps + " mbps");
  }
}

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