[FEATURE] Accessibility - Add unique titles to frames

[frankspin89]

Expected Behavior

Frames must have unique title attribute
https://dequeuniversity.com/rules/axe/1.1/frame-title

Current Behavior

<iframe class="chartjs-hidden-iframe" tabindex="-1" style="display: block; overflow: hidden; border: 0px; margin: 0px; top: 0px; left: 0px; bottom: 0px; right: 0px; height: 100%; width: 100%; position: absolute; pointer-events: none; z-index: -1;">

Possible Solution

<iframe title="Unique title goes here" class="chartjs-hidden-iframe" tabindex="-1" style="display: block; overflow: hidden; border: 0px; margin: 0px; top: 0px; left: 0px; bottom: 0px; right: 0px; height: 100%; width: 100%; position: absolute; pointer-events: none; z-index: -1;">

[devjeetr]

I'm new to contributing to this project but I've been looking at this issue and I was thinking we could use the uid of each chart to create this unique title. One way to do this would be to modify createResizer() to accept chart id as the second argument. So we would have to change this:

    function createResizer(handler) {
	    var iframe = document.createElement('iframe');
            iframe.className = 'chartjs-hidden-iframe';

to something like:

    function createResizer(handler, chartId) {
	    var iframe = document.createElement('iframe');
	    iframe.title = 'Resizer Frame for Chart ' + chartId;
	    iframe.className = 'chartjs-hidden-iframe';

Also, inside addResizeListener, we would have to change the call to createResizer:

function addResizeListener(node, listener, chart){
   // ....
   stub.resizer = createResizer(notify, chart.id);

Any thoughts? I'm very new to this project so forgive me if I'm missing something major in here.

[simonbrunel]

@devjeetr I don't think the resizer should be bound to the chart id since it will soon be possible to share the same resizer between multiple charts. Instead, I would keep it simple and set a generic (and short) title (e.g. title="chartjs-iframe"). Anyway, this iframe is going to be replaced by divs hopefully soon.

[simonbrunel]

@frankspin89 @devjeetr starting #4596, we don't use IFRAME anymore