Develop Reference

Photoshop javascript batch replace smart layer from folder and resize

I am trying to work out how to use javascript with photoshop, but eventhough i dont find a logical error in the code, it doesnt work properly.
I have a folder of 1000+ images/.ai files that have varying dimensions. I need these images on the Pillow and saved as .jpeg.
I choose the smartlayer and run the script to choose the images and it saves them correctly. The only problem is, that the resizing of images and positioning dont work properly.
If i put the image in manually, it works without issues, but not with the script.
If the width is greater than the height, it should set the width to 1200 px and calculate the height according to that. (and vice versa) and place in the middle of the layer.
How do i fix the resizing and positioning?
Is it possible to choose a folder where the images are inside instead of selecting the images?
How do i handle it when there are 2 smart layers to change in the mockup instead of 1?
Anyone know where the problem lies this code?
Im grateful for any bit of help!
// Replace SmartObject’s Content and Save as JPG
// 2017, use it at your own risk
// Via #Circle B: https://graphicdesign.stackexchange.com/questions/92796/replacing-a-smart-object-in-bulk-with-photoshops-variable-data-or-scripts/93359
// JPG code from here: https://forums.adobe.com/thread/737789
#target photoshop
if (app.documents.length > 0) {
var myDocument = app.activeDocument;
var theName = myDocument.name.match(/(.*)\.[^\.]+$/)[1];
var thePath = myDocument.path;
var theLayer = myDocument.activeLayer;
// JPG Options;
jpgSaveOptions = new JPEGSaveOptions();
jpgSaveOptions.embedColorProfile = true;
jpgSaveOptions.formatOptions = FormatOptions.STANDARDBASELINE;
jpgSaveOptions.matte = MatteType.NONE;
jpgSaveOptions.quality = 8;
// Check if layer is SmartObject;
if (theLayer.kind != "LayerKind.SMARTOBJECT") {
alert("selected layer is not a smart object")
} else {
// Select Files;
if ($.os.search(/windows/i) != -1) {
var theFiles = File.openDialog("please select files", "*.psd;*.tif;*.jpg;*.ai", true)
} else {
var theFiles = File.openDialog("please select files", getFiles, true)
};
};
(function (){
var startRulerUnits = app.preferences.rulerUnits;
app.preferences.rulerUnits = Units.PIXELS;
var bounds = activeDocument.activeLayer.bounds;
var height = bounds[3].value - bounds[1].value;
var width = bounds[2].value - bounds[0].value;
if (height > width){
var newSize1 = (100 / width) * 800;
activeDocument.activeLayer.resize(newSize1, newSize1, AnchorPosition.MIDDLECENTER);
app.preferences.rulerUnits = startRulerUnits;
}
else{
var newSize2 = (100 / height) * 800;
activeDocument.activeLayer.resize(newSize2, newSize2, AnchorPosition.MIDDLECENTER);
app.preferences.rulerUnits = startRulerUnits;
}
})();
if (theFiles) {
for (var m = 0; m < theFiles.length; m++) {
// Replace SmartObject
theLayer = replaceContents(theFiles[m], theLayer);
var theNewName = theFiles[m].name.match(/(.*)\.[^\.]+$/)[1];
// Save JPG
myDocument.saveAs((new File(thePath + "/" + theName + "_" + theNewName + ".jpg")), jpgSaveOptions, true,Extension.LOWERCASE);
}
}
};
// Get PSDs, TIFs and JPGs from files
function getFiles(theFile) {
if (theFile.name.match(/\.(psd|tif|jpg)$/i) != null || theFile.constructor.name == "Folder") {
return true
}
};
// Replace SmartObject Contents
function replaceContents(newFile, theSO) {
app.activeDocument.activeLayer = theSO;
// =======================================================
var idplacedLayerReplaceContents = stringIDToTypeID("placedLayerReplaceContents");
var desc3 = new ActionDescriptor();
var idnull = charIDToTypeID("null");
desc3.putPath(idnull, new File(newFile));
var idPgNm = charIDToTypeID("PgNm");
desc3.putInteger(idPgNm, 1);
executeAction(idplacedLayerReplaceContents, desc3, DialogModes.NO);
return app.activeDocument.activeLayer
};
I have attached 2 pictures. 1 how it needs to look like and 2 what the script outputs
Correct
Wrong

Your replaced images have to be the same resolution as the smart object.
You can declare the folder path in your code. If you still want to select the path by hand, you can select one image in the path, and extract the parent folder path.
You can recursively go through all of the layers in the documents and extract all the smart objects that you want to replace.
You may want a function to recursively traverse all the layers in the document
function browseLayer(layer, fn) {
if (layer.length) {
for (var i = 0; i < layer.length; ++i) {
browseLayer(layer[i], fn)
}
return;
}
if (layer.layers) {
for (var j = 0; j < layer.layers.length; ++j) {
browseLayer(layer.layers[j], fn);
}
return;
}
//apply this function for every layer
fn(layer)
}
Get all the smart objects in the document
const smartObjects = [];
//The smart objects can be visit twice or more
//use this object to mark the visiting status
const docNameIndex = {};
const doc = app.open(new File("/path/to/psd/file"));
browseLayer(doc.layers, function (layer) {
//You cannot replace smart object with position is locked
if (layer.kind == LayerKind.SMARTOBJECT && layer.positionLocked == false) {
smartLayers.push(layer);
doc.activeLayer = layer;
//open the smart object
executeAction(stringIDToTypeID("placedLayerEditContents"), new ActionDescriptor(), DialogModes.NO);
//activeDocument is now the smart object
const docName = app.activeDocument.name;
if (!docNameIndex[docName]) {
docNameIndex[docName] = true;
smartObjects.push({
id: layer.id,
name: layer.name,
docName: docName,
width : app.activeDocument.width.as('pixels'),
height : app.activeDocument.height.as('pixels'),
resolution : app.activeDocument.resolution //important
});
}
//reactive the main document
app.activeDocument = doc;
}
});
I assume that you have two smart objects needed to replace, the images for replacement are stored in different folders with the same name.
smartObjects[0].replaceFolderPath = "/path/to/folder/1";
smartObjects[1].replaceFolderPath = "/path/to/folder/2";
//we need temp folder to store the resize images
smartObjects[0].tempFolderPath = "/path/to/temp/folder/1";
smartObjects[1].tempFolderPath = "/path/to/temp/folder/2";
Ex: The first iteration will replace smartObjects[0] with "/path/to/folder/1/image1.jpg", and smartObjects[1] with "/path/to/folder/image1.jpg"
Now resize all the images following the properties of the smart objects
smartObjects.forEach(function(smartObject){
//Get all files in the folder
var files = new Folder(smartObject.replaceFolderPath).getFiles();
//Resize all the image files
files.forEach(function (file) {
var doc = app.open(file);
doc.resizeImage(
new UnitValue(smartObject.width + ' pixels'),
new UnitValue(smartObject.height + ' pixels'),
smartObject.resolution
);
//save to temp folder
doc.saveAs(
new File(smartObject.tempFolderPath + "/" + file.name),
new PNGSaveOptions(),
true
);
doc.close(SaveOptions.DONOTSAVECHANGES)
});
});
Finally, replace the smart object
//get list of file again
var files = new Folder(smartObject.replaceFolderPath).getFiles();
files.forEach(function(file){
var fileName = file.name;
smartObjects.forEach(function(smartObject){
//active the window opening the smart object
app.activeDocument = app.documents.getByName(args.documentName);
var desc = new ActionDescriptor();
desc.putPath(charIDToTypeID("null"), new File(smartObject.tempFolderPath + "/" + fileName));
executeAction(stringIDToTypeID( "placedLayerReplaceContents" ), desc, DialogModes.NO);
});
//Now export document
var webOptions = new ExportOptionsSaveForWeb();
webOptions.format = SaveDocumentType.PNG; // SaveDocumentType.JPEG
webOptions.optimized = true;
webOptions.quality = 100;
doc.exportDocument(new File("/path/to/result/folder" + file.name), ExportType.SAVEFORWEB, webOptions);
});
Now you can close all the opening smart objects
smartObjects.forEach(function (s) {
app.documents.getByName(r.docName).close(SaveOptions.DONOTSAVECHANGES);
});

readAsArrayBuffer is extremely slow on mobile

Run the snippet below on desktop browser and select any file over 10MB. You will get read speed around 4MB/s. If you run it on mobile Chrome in android you will get something near 90Kb/s.
Is there a way it can be improved?
p.s.
I'm using sliceFile to send BufferArray over RTCDataChannel from mobile.
function load() {
function bytesToSize(bytes) {
var sizes = ['Bytes/s', 'KB/s', 'MB/s', 'GB/s', 'TB/s'];
if (bytes < 1) return '';
var i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
return Math.round(bytes / Math.pow(1024, i), 2) + ' ' + sizes[i];
}
var reader = new window.FileReader();
var offset = 0;
var f = window.event.target.files[0];
proggress.max = f.size;
reader.onload = read;
function read() {
if (offset < f.size) {
var currentSlice = f.slice(offset, offset + 16384);
offset += 16384;
reader.readAsArrayBuffer(currentSlice);
proggress.value = offset;
}
}
var lastOffset = 0;
setInterval(function () {
var s = bytesToSize(offset - lastOffset);
if (s) {
currSpeed.textContent = s;
}
lastOffset = offset;
}, 1000);
read();
}
<progress id="proggress"></progress>
<div id="currSpeed"></div>
<input type="file" value="click" onchange="load()"/>
UPDATE:
I ended up with slicing bigger chunks and splitting them manually from ArrayBuffer into required ones.

Strip EXIF data from image

How can I strip the EXIF data from an uploaded image through javascript? I am currently able to access the EXIF data using this exif-js plugin, like this:
EXIF.getData(oimg, function() {
var orientation = EXIF.getTag(this, "Orientation");
});
However, I have not found any way to actually remove the Exif data, only to retrieve it.
More specifically, I am trying to do this to get rid of the orientation Exif data which rotates my image on certain browsers.

look up the file format and exif format
read the file into arraybuffer
find the required data and remove it
create a blob from the remaining data
upload it with ajax
Here is a little demo of it, select an image with orientation data to see how it looks with and with out it(modern browsers only).
http://jsfiddle.net/mowglisanu/frhwm2xe/3/
var input = document.querySelector('#erd');
input.addEventListener('change', load);
function load(){
var fr = new FileReader();
fr.onload = process;
fr.readAsArrayBuffer(this.files[0]);
document.querySelector('#orig').src = URL.createObjectURL(this.files[0]);
}
function process(){
var dv = new DataView(this.result);
var offset = 0, recess = 0;
var pieces = [];
var i = 0;
if (dv.getUint16(offset) == 0xffd8){
offset += 2;
var app1 = dv.getUint16(offset);
offset += 2;
while (offset < dv.byteLength){
//console.log(offset, '0x'+app1.toString(16), recess);
if (app1 == 0xffe1){
pieces[i] = {recess:recess,offset:offset-2};
recess = offset + dv.getUint16(offset);
i++;
}
else if (app1 == 0xffda){
break;
}
offset += dv.getUint16(offset);
var app1 = dv.getUint16(offset);
offset += 2;
}
if (pieces.length > 0){
var newPieces = [];
pieces.forEach(function(v){
newPieces.push(this.result.slice(v.recess, v.offset));
}, this);
newPieces.push(this.result.slice(recess));
var br = new Blob(newPieces, {type: 'image/jpeg'});
document.querySelector('#mod').src = URL.createObjectURL(br);
}
}
}
img{
max-width:200px;
}
<input id="erd" type="file"/><br>
<img id="orig" title="Original">
<img id="mod" title="Modified">

javascript suppress error and continue in for loop

I'm trying to implement a speedtest by downloading 3 image files from the internet, and averaging the time it took to load them. If there is an error for whatever reason, I want to skip loading that image and proceed with the next one. If the error occurs on the last image, then I want to calculate the average speed at that point and return to the caller.
Right now, once an error occurs (I deliberately changed the url of an image so it doesn't exist), it won't go further. I've tried returning true from the .onerror function, but no luck. Any suggestions?
var images = [{
"url": 'http://<removed>250k.jpg?n=' + Math.random(),
"size": 256000
}, {
"url": 'http://<removed>500k.jpg?n=' + Math.random(),
"size": 512000
}, {
"url": '<removed>1000k.jpg?n=' + Math.random(),
"size": 1024000
}
];
function calculateBandwidth() {
var results = [];
for (var i = 0; i < images.length; i++) {
var startTime, endTime;
var downloadSize = images[i].size;
var download = new Image();
download.onload = function () {
endTime = (new Date()).getTime();
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);
results.push(speedMbps);
//Calculate the average speed
if (results.length == 3) {
var avg = (parseFloat(results[0]) + parseFloat(results[1]) + parseFloat(results[2])).toFixed(2);
return avg;
}
}
download.onerror = function (e) {
console.log("Failed to load image!");
return true;
};
startTime = (new Date()).getTime();
download.src = images[i].url;
}
}

I think what you're not doing is controlling the process as each event occurs. Each onerror and onload tells you that the process stopped, not that it should quit per se. You initialize one image, it doesn't load, maybe take note, otherwise continue.
The thing is, you do the same thing at the end of onload too. That is, do whatever measurements, then move to the next or, if no more, run the script that cleans up and reports or whatnot.
For instance:
var site = 'http://upload.wikimedia.org/',
imgs = [
'wikipedia/commons/6/6e/Brandenburger_Tor_2004.jpg',
'wikipedia/commons/a/ad/Cegonha_alsaciana.jpg',
'wikipe/Cegonha_alsaciana.jpg',
'wikipedia/commons/d/da/CrayonLogs.jpg',
'wikipedia/commons/1/17/Bobbahn_ep.jpg',
'wikipedia/commons/9/90/DS_Citro%C3%ABn.jpg',
'wikipedia/commons/f/f0/DeutzFahr_Ladewagen_K_7.39.jpg',
'wikipedia/commons/c/c7/DenglerSW-Peach-faced-Lovebird-20051026-1280x960.jpg',
'wikipedia/commons/4/4d/FA-18F_Breaking_SoundBarrier.jpg'
];
My array of images. Hint, wikipe/Cegonha_alsaciana.jpg won't load. Be forewarned, these are large and load slowly and I use a cache buster to keep them firing onloads.
getimg();
In the fiddle, this is all within a window.onload event handler, so when that gets called, this initializes the process. I don't have a setup phase, per se, or otherwise I might have called it init() or setup().
function getimg() {
var img = document.createElement('img'),
path = imgs.shift();
if (path) {
img.onload = loaded;
img.onerror = notloaded;
img.src = site + path + '?cach=bust' + Math.floor(Math.random() * 9999);
console.log('Loading ', img.src);
document.body.appendChild(img);
} else {
console.log('Finished loading images.');
}
function loaded(e) {
console.log('Loaded ', e.target.src);
next();
}
function notloaded(e) {
console.log('Not loaded ', e.target.src);
next();
}
function next() {
console.log(imgs.length, ' imgs left to load.');
getimg();
}
}
http://jsfiddle.net/userdude/vfTfP/
This does what you're trying to do, without the timing mechanism built-in. I can break things off into steps, actions and events, so that I can control the steps as necessary. In a basic way, your script should not run much differently.

How to detect internet speed in JavaScript?

How can I create a JavaScript page that will detect the user’s internet speed and show it on the page? Something like “your internet speed is ??/?? Kb/s”.

It's possible to some extent but won't be really accurate, the idea is load image with a known file size then in its onload event measure how much time passed until that event was triggered, and divide this time in the image file size.
Example can be found here: Calculate speed using javascript
Test case applying the fix suggested there:
//JUST AN EXAMPLE, PLEASE USE YOUR OWN PICTURE!
var imageAddr = "http://www.kenrockwell.com/contax/images/g2/examples/31120037-5mb.jpg";
var downloadSize = 4995374; //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>
Quick comparison with "real" speed test service showed small difference of 0.12 Mbps when using big picture.
To ensure the integrity of the test, you can run the code with Chrome dev tool throttling enabled and then see if the result matches the limitation. (credit goes to user284130 :))
Important things to keep in mind:
The image being used should be properly optimized and compressed. If it isn't, then default compression on connections by the web server might show speed bigger than it actually is. Another option is using uncompressible file format, e.g. jpg. (thanks Rauli Rajande for pointing this out and Fluxine for reminding me)
The cache buster mechanism described above might not work with some CDN servers, which can be configured to ignore query string parameters, hence better setting cache control headers on the image itself. (thanks orcaman for pointing this out))
The bigger the image size is, the better. Larger image will make the test more accurate, 5 mb is decent, but if you can use even a bigger one it would be better.

Well, this is 2017 so you now have Network Information API (albeit with a limited support across browsers as of now) to get some sort of estimate downlink speed information:
navigator.connection.downlink
This is effective bandwidth estimate in Mbits per sec. The browser makes this estimate from recently observed application layer throughput across recently active connections. Needless to say, the biggest advantage of this approach is that you need not download any content just for bandwidth/ speed calculation.
You can look at this and a couple of other related attributes here
Due to it's limited support and different implementations across browsers (as of Nov 2017), would strongly recommend read this in detail

I needed a quick way to determine if the user connection speed was fast enough to enable/disable some features in a site I’m working on, I made this little script that averages the time it takes to download a single (small) image a number of times, it's working pretty accurately in my tests, being able to clearly distinguish between 3G or Wi-Fi for example, maybe someone can make a more elegant version or even a jQuery plugin.
var arrTimes = [];
var i = 0; // start
var timesToTest = 5;
var tThreshold = 150; //ms
var testImage = "http://www.google.com/images/phd/px.gif"; // small image in your server
var dummyImage = new Image();
var isConnectedFast = false;
testLatency(function(avg){
isConnectedFast = (avg <= tThreshold);
/** output */
document.body.appendChild(
document.createTextNode("Time: " + (avg.toFixed(2)) + "ms - isConnectedFast? " + isConnectedFast)
);
});
/** test and average time took to download image from server, called recursively timesToTest times */
function testLatency(cb) {
var tStart = new Date().getTime();
if (i<timesToTest-1) {
dummyImage.src = testImage + '?t=' + tStart;
dummyImage.onload = function() {
var tEnd = new Date().getTime();
var tTimeTook = tEnd-tStart;
arrTimes[i] = tTimeTook;
testLatency(cb);
i++;
};
} else {
/** calculate average of array items then callback */
var sum = arrTimes.reduce(function(a, b) { return a + b; });
var avg = sum / arrTimes.length;
cb(avg);
}
}

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.
That said, point-in-time bandwidth tests are notoriously unreliable, being as they are impacted by other items being downloaded in other windows, the speed of your server, links en route, etc., etc. But you can get a rough idea using this sort of technique.

Even though this is old and answered, i´d like to share the solution i made out of it 2020 base on Shadow Wizard Says No More War´s solution
I just merged it into an object that comes with the flexibility to run at anytime and run a callbacks if the specified mbps is higher or lower the measurement result.
you can start the test anywhere after you included the testConnectionSpeed Object by running the
/**
* #param float mbps - Specify a limit of mbps.
* #param function more(float result) - Called if more mbps than specified limit.
* #param function less(float result) - Called if less mbps than specified limit.
*/
testConnectionSpeed.run(mbps, more, less)
for example:
var testConnectionSpeed = {
imageAddr : "https://upload.wikimedia.org/wikipedia/commons/a/a6/Brandenburger_Tor_abends.jpg", // this is just an example, you rather want an image hosted on your server
downloadSize : 2707459, // Must match the file above (from your server ideally)
run:function(mbps_max,cb_gt,cb_lt){
testConnectionSpeed.mbps_max = parseFloat(mbps_max) ? parseFloat(mbps_max) : 0;
testConnectionSpeed.cb_gt = cb_gt;
testConnectionSpeed.cb_lt = cb_lt;
testConnectionSpeed.InitiateSpeedDetection();
},
InitiateSpeedDetection: function() {
window.setTimeout(testConnectionSpeed.MeasureConnectionSpeed, 1);
},
result:function(){
var duration = (endTime - startTime) / 1000;
var bitsLoaded = testConnectionSpeed.downloadSize * 8;
var speedBps = (bitsLoaded / duration).toFixed(2);
var speedKbps = (speedBps / 1024).toFixed(2);
var speedMbps = (speedKbps / 1024).toFixed(2);
if(speedMbps >= (testConnectionSpeed.max_mbps ? testConnectionSpeed.max_mbps : 1) ){
testConnectionSpeed.cb_gt ? testConnectionSpeed.cb_gt(speedMbps) : false;
}else {
testConnectionSpeed.cb_lt ? testConnectionSpeed.cb_lt(speedMbps) : false;
}
},
MeasureConnectionSpeed:function() {
var download = new Image();
download.onload = function () {
endTime = (new Date()).getTime();
testConnectionSpeed.result();
}
startTime = (new Date()).getTime();
var cacheBuster = "?nnn=" + startTime;
download.src = testConnectionSpeed.imageAddr + cacheBuster;
}
}
// start test immediatly, you could also call this on any event or whenever you want
testConnectionSpeed.run(1.5, function(mbps){console.log(">= 1.5Mbps ("+mbps+"Mbps)")}, function(mbps){console.log("< 1.5Mbps("+mbps+"Mbps)")} )
I used this successfuly to load lowres media for slow internet connections. You have to play around a bit because on the one hand, the larger the image, the more reasonable the test, on the other hand the test will take way much longer for slow connection and in my case I especially did not want slow connection users to load lots of MBs.

The image trick is cool but in my tests it was loading before some ajax calls I wanted to be complete.
The proper solution in 2017 is to use a worker (http://caniuse.com/#feat=webworkers).
The worker will look like:
/**
* 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
);
};
The js file that will invoke the Worker:
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);
}
};
Code taken from a Plone package I wrote:
https://github.com/collective/experimental.bwtools/blob/master/src/experimental/bwtools/browser/static/scripts/

It's better to use images for testing the speed. But if you have to deal with zip files, the below code works.
var fileURL = "your/url/here/testfile.zip";
var request = new XMLHttpRequest();
var avoidCache = "?avoidcache=" + (new Date()).getTime();;
request.open('GET', fileURL + avoidCache, true);
request.responseType = "application/zip";
var startTime = (new Date()).getTime();
var endTime = startTime;
request.onreadystatechange = function () {
if (request.readyState == 2)
{
//ready state 2 is when the request is sent
startTime = (new Date().getTime());
}
if (request.readyState == 4)
{
endTime = (new Date()).getTime();
var downloadSize = request.responseText.length;
var time = (endTime - startTime) / 1000;
var sizeInBits = downloadSize * 8;
var speed = ((sizeInBits / time) / (1024 * 1024)).toFixed(2);
console.log(downloadSize, time, speed);
}
}
request.send();
This will not work very well with files < 10MB. You will have to run aggregated results on multiple download attempts.

thanks to Punit S answer, for detecting dynamic connection speed change, you can use the following code :
navigator.connection.onchange = function () {
//do what you need to do ,on speed change event
console.log('Connection Speed Changed');
}

Improving upon John Smith's answer, a nice and clean solution which returns a Promise and thus can be used with async/await. Returns a value in Mbps.
const imageAddr = 'https://upload.wikimedia.org/wikipedia/commons/a/a6/Brandenburger_Tor_abends.jpg';
const downloadSize = 2707459; // this must match with the image above
let startTime, endTime;
async function measureConnectionSpeed() {
startTime = (new Date()).getTime();
const cacheBuster = '?nnn=' + startTime;
const download = new Image();
download.src = imageAddr + cacheBuster;
// this returns when the image is finished downloading
await download.decode();
endTime = (new Date()).getTime();
const duration = (endTime - startTime) / 1000;
const bitsLoaded = downloadSize * 8;
const speedBps = (bitsLoaded / duration).toFixed(2);
const speedKbps = (speedBps / 1024).toFixed(2);
const speedMbps = (speedKbps / 1024).toFixed(2);
return Math.round(Number(speedMbps));
}

I needed something similar, so I wrote https://github.com/beradrian/jsbandwidth. This is a rewrite of https://code.google.com/p/jsbandwidth/.
The idea is to make two calls through Ajax, one to download and the other to upload through POST.
It should work with both jQuery.ajax or Angular $http.

//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>

Mini snippet:
var speedtest = {};
function speedTest_start(name) { speedtest[name]= +new Date(); }
function speedTest_stop(name) { return +new Date() - speedtest[name] + (delete
speedtest[name]?0:0); }
use like:
speedTest_start("test1");
// ... some code
speedTest_stop("test1");
// returns the time duration in ms
Also more tests possible:
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"