How to check the integrity of loaded Javascript code

Question

I run a Bitcoin wallet that uses browser side Javascript to encrypt and decrypt Bitcoin keys.

I want to make the javascript available for scrutiny on Github, and then load the javascript from the github repository.

My problem is I need to check the integrity of the loaded Javascript to ensure at hasn't been tampered with at Github.

How can I best do this ? Would it be something like.

1. Load remote Javascript with an ajax call.
2. MD5 hash and compare.
3. If in good shape execute it.

Answer 1

There is (or soon WILL be) an elegant way to achieve this now (2 years after the question was asked).

http://www.w3.org/TR/SRI/

You can now specify the "integrity" parameter inside the script tag:

<script src="https://github.com/<path>/yourscript.js"
        integrity="sha256-SDf......">

This won't work for the script loaded via an AJAX requests. But you can potentially reference scripts as script tags pointing at the CDN (ideally not at github directly)