I just set srcdoc attribute to iframe equals url in AjaxUpload component.

iframe.setAttribute('srcdoc', this._settings.action);

It's solved my problem.

Function into file AjaxUpload.js:

        _createIframe: function(){
            var id = getUID();            

            var iframe = toElement('<iframe src="javascript:false;" name="' + id + '" />');        
            iframe.setAttribute('id', id);
            iframe.setAttribute('srcdoc', this._settings.action);

            iframe.style.display = 'none';
            document.body.appendChild(iframe);

            return iframe;
        }

This answer helped me patch our copy of Atmail so uploading attachments works again in Chrome 83 - thanks!

The above setAttribute line should be inserted into the AjaxUpload.js file, inside the '_createIframe' function. I put it immediately below the setAttribute('id', id) call and that has done the trick :)

The problem is that the library is creating an <iframe>, with an src attribute, and listens for the load event of that iframe right after it did.

/**
* Creates iframe with unique name
*/
_createIframe: function () {
    // unique name
    // We cannot use getTime, because it sometimes return
    // same value in safari :(
    var id = getUID();

    // Remove ie6 "This page contains both secure and nonsecure items" prompt 

    var iframe = toElement('<iframe src="javascript:false;" name="' + id + '" />');
    iframe.id = id;
    iframe.style.display = 'none';
    d.body.appendChild(iframe);
    return iframe;
},

then in submit method

            var iframe = this._createIframe();

            // some synchronous operations

            addEvent(iframe, 'load', function (e) { // ...

Since this iframe has an src attribute, Chrome will start its loading, and since its src is a fake url, this operation actually is resolved synchronously, meaning that the load event is already set to fire at the next event-loop iteration.

const frame = document.createElement('iframe');
frame.src = 'javascript:return false';
document.body.append(frame);
frame.addEventListener('load', (evt) => console.log('loaded', frame.src) );

setTimeout( () => frame.src = "about:blank", 0 );

// Results in Chrome:
// loaded javascript:return false
// loaded about:blank

// Results in Firefox:
// loaded about:blank

So the one load event this library is receiving is that initial load event, of an empty document, and not the one of the real request.

To fix that, all you need is to remove this src="javascript:false;" from the library code: https://jsfiddle.net/9phxmqjw/

We were using this old plugin:

http://jquery.malsup.com/form/#options-object

There's an option there you might be using if you were supporting ie8 at some point in the past 10 years...

{
    url: '/branded/image_upload',
    type: 'POST',
    iframe: false
}

We also had a <textarea></textarea> wrapper hack in the response.

This code was passed down through a lot of iterations lol.

Thank You! Also, for all still using Opencart 1.5 after this Chrome Update, image and document upload is fixed by adding:

iframe.setAttribute('srcdoc', this._settings.action);

in \admin\view\javascript\jquery\ajaxupload.js

var iframe = toElement('<iframe src="javascript:false;" name="' + id + '" />');
            // src="javascript:false; was added
            // because it possibly removes ie6 prompt 
            // "This page contains both secure and nonsecure items"
            // Anyway, it doesn't do any harm.
            iframe.setAttribute('id', id);
            iframe.setAttribute('srcdoc', this._settings.action);
            iframe.style.display = 'none';
            document.body.appendChild(iframe);