use Fetch API where available (Firefox, Chrome, Opera)

[nschloe]

Right now, pdf.js uses XMLHttpRequest (XHR) for fetching the PDF, see https://github.com/mozilla/pdf.js/blob/master/src/core/network.js.

With the recent development of the Fetch API (released in Chrome 42, Firefox 39, Opera 30), a clean replacement for XHR is now in place; see

• https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/,
• http://davidwalsh.name/fetch,
• https://github.com/GoogleChrome/samples/blob/gh-pages/fetch-api/fetch-response-stream.html.

It can easily be detected if the current browser has fetch(), so this indeed looks like a interesting alternative.

[timvandermeij]

Interesting, that sounds awesome. If someone is willing to work on this, feel free to submit a pull request. We must be sure to remain compatible for old browsers, so we probably need a fallback to XHR or a polyfill for fetch() to do so.

[yurydelendik]

Dup of #5319 ?

[existentialism]

Also #6126

[timvandermeij]

Right, closing as duplicate of #6126. Let's continue there.