IE11 error: startsWith not supported

[stefano-1973]

The normalizeUrl and calculatePageTokenForUri functions in csrfguard.js use a function not supported by IE11: startsWith
For example in the js file there is this:

let normalizedUrl = url.startsWith('/') ? url : '/' + url;

I see that you have already created the function startsWith(s, prefix) but you have not used it in the above instruction (and other places)

[forgedhallpass]

#31 would also solve this issue implicitly.

[stefano-1973]

I've created the pull request #37 for this issue

[forgedhallpass]

Thanks @stefano-1973. Congrats for your first contribution!

Thinking out loud, I believe polyfills would have been another viable solution. The console.debugs should rather be removed through minification and the generated JS should be used in production instead, but this will be handled in #31 then.