Vaadin-grid: Replace iron-ajax with fetch in demos

[marcushellberg]

Several demos use <iron-ajax> for fetching data. As of P3, when the component is a JS file, it feels very strange to define the data fetching as HTML inside of a string instead of using fetch directly in JS.

Using fetch would also make the demos less Polymer bound and easier to approach for non-Polymer devs.

[moderndeveloperllc]

@marcushellberg Y'all just need to make vaadin-ajax that uses fetch under it all ;-)

[marcushellberg]

Haha. I'm still not sold on declarative AJAX 😀I could still somehow accept it when Polymer Components were HTML files, as you could fetch some data without writing any JS. But now, when you're already in JS, writing a template as a string to essentially do a JS call just feels... backwards.

[moderndeveloperllc]

@marcushellberg Honestly, I just like the ancillary functions around debouncing, query string encoding, lifecycle event firing, etc. I already have a custom component for my API calls that does a

this.request = document.createElement('iron-ajax');

I'll probably switch that over to fetch at some point in time, but that would mean recreating all the above functions, or finding a good npm package that already does.

[tomivirkki]

The demo files are loaded dynamically, so the source must be in ES5 (in order for them to function on IE11)

[web-padawan]

We can consider using fetch polyfill but need to make sure it would be properly loaded by demos hosted on https://vaadin.com

[tomivirkki]

The demos have been updated and <iron-ajax> is no longer used. The one demo that fetches data from an external source uses XHRs https://cdn.vaadin.com/vaadin-grid/5.2.0-alpha4/demo/#grid-data-demos