chore(docs): speed up app initialization

[petebacondarwin]

It takes an unreasonable amount of time for the docs app to initialize. On a desktop we are talking up to 4 secs - on a phone or lower power machine it can be up to 20 secs!

Some investigation:

• we need to be able to provide a number of the larger files zipped up if the browser supports it - this primarily involves configuring the server
• we need to provide better cache expiration values to allow browsers to cache more effectively - this involves configuring the server but may also require dgeni (or some other tool) to append cache busting extras onto the file paths
• we are downloading a large file (pages-data.js) containing mappings of page paths to partials (and titles). In reality a small configuration change to dgeni-packages and we could have a straightforward one-to-one mapping between page paths and their partials. If the partial also then contained the page title and breadcrumb information then we would not need to have all this large file.
• the lunr full text search is the main cause of the delay in loading - it is building the search index every time from information in the pages-data.js file. We need a way to optimize this and/or move it from the main initial rendering thread, since the rendering is blocking until this has completed.

Lunr Search

The search index is generated on page load from a set of terms in the pages-data.js file. This file is large (~470Kb) and currently the app is blocking on this downloading. The search index generation takes a number of seconds and the JavaScript loop is blocked while this is happening. Currently this is happening at application bootstrap.

Load the data asynchronously

The obvious initial idea is to move the data into a file that is loaded via $http after the application has bootstrapped, since this will allow the initial page to render while we wait for the data to arrive.

Process the data in a WebWorker

Second, since the actual processing takes some time, we could consider moving the processing into a WebWorker for browsers that support it.

Cache the data in LocalStorage

Finally, we could consider caching the index in the LocalStorage, if available. This would require us to be able to work out how to invalidate the cache when the index is stale. Perhaps we should just store the index keyed on the version of Angular. We could use an LRU cache algorithm.

[caitp]

what if we generated this stuff from Workers? (non-nested) WebWorkers are available on almost all target browsers. Then at least we wouldn't be blocking execution on the main thread, although we could wait for the search index to be built if a user tries to search before it's ready.

Ontop of that, we could be doing a better job of caching this stuff, I like the localStorage idea. We'd want to use a cache key which includes the version/build number, I think.

Seems doable

[petebacondarwin]

I think those were in my second and third points. Glad we are on the same page.

[caitp]

I didn't read the whole post, it's long =)