Browser HTTP queue test

This page demonstrates a bug in Chrome, whereby rendering of cached images are blocked by AJAX requests.

The image cat.jpg has far-future cache headers, and is retrieved by AJAX when the page is loaded. Therefore it is in the browsers cache, and will not be re-retrieved from the server. The image cat2.png has no-cache headers.

Pressing Start test does the following:

• Starts the provided number of concurrent AJAX requests to a URL which takes 2 seconds to respond
• Immediately afterwards, adds an <img> element pointing to cat.jpg (cached) or cat2.png (uncached).

Expected behavior (tested in Firefox, IE10, Android 4.4): The image renders immediately, since it is in the cache. AJAX requests return progressively.

Actual behavior (tested in Chrome 49/Linux, Chrome 49/Win, Chromium 48/Linux, Chrome/Android 5.1.1):

• The first time, Chrome puts the image in the request queue even though it's already in the cache. The image does not render until sufficiently many AJAX requests are done, even though it never makes a request to the server.
• Later times (or if an <img> element has been created with the URL) the image is rendered immediately. Evidently Chrome remembers that it has this image and renders it.