Delay setting src attribute after <img> is in DOM to prevent extraneous image loading #176
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This is an interesting problem: some browsers (FF, Safari, but not Chrome) would load an image immediately one you set the `src` attribute of `<img>`. While this is expected (think of programmatically preloading images), it poses a problem when you actually want to use the `<img>` as a child of `<picture>`, as the `src` attribute represents the fallback for browsers not supporting `<source>`. But this is actually what happens if you render the markup in Ember: it creates the element detached from DOM (`document.createElement()`), sets the attributes (`element.setAttribute()`) and only after that attaches it to its parent. Chrome handles this more cleverly, but FF would (upon setting `src`) load the fallback image (jpeg), later sees the better `<source>` alternative (e.g. webp) and would load that *also*. Note that this does *not* happen, when the `<img>` is already part of `<picture>`, as the browser probably can understand now that the `src` attribute is not the only possible image URL. Also all of that does not happen in a server-rendered HTML page (FastBoot, or any other server-rendered page), only when JS/Ember re-renders the page with JavaScript would that wrong behaviour show up again. The solution seems simple enough: delay setting `src` until the `<img>` is in DOM and part of `<picture>`.
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This is an interesting problem: some browsers (FF, Safari, but not Chrome) would load an image immediately once you set the
srcattribute of<img>. While this is expected (think of programmatically preloading images), it poses a problem when you actually want to use the<img>as a child of<picture>, as thesrcattribute represents the fallback for browsers not supporting<source>.But this is actually what happens if you render the markup in Ember: it creates the element detached from DOM (
document.createElement()), sets the attributes (element.setAttribute()) and only after that attaches it to its parent. Chrome handles this more cleverly, but FF would (upon settingsrc) load the fallback image (jpeg), later sees the better<source>alternative (e.g. webp) and would load that also. Note that this does not happen, when the<img>is already part of<picture>, as the browser probably can understand now that thesrcattribute is not the only possible image URL.Also all of that does not happen in a server-rendered HTML page (FastBoot, or any other server-rendered page), only when JS/Ember re-renders the page with JavaScript would that wrong behaviour show up again.
The solution seems simple enough: delay setting
srcuntil the<img>is in DOM and part of<picture>.