Several js functions in our gem don't follow our js module pattern

[owenatgov]

We have several legacy functions which are structured differently from our typical module js pattern eg: as IIFE's (Immediately Invoked Function Expression). These are:

• [x] header-navigation
• [ ] cookie-function
• [ ] current-location
• [ ] primary-links
• [ ] trigger-event
• [ ] govspeak/barchart-enhancement
• [ ] govspeak/youtube-link-enhancement

This causes a couple of issues:

• It is in conflict with our convention of using the javascript module pattern to initialise our js
• It is possible to initialise twice if imported in 2 separate places (example of issue https://github.com/alphagov/static/pull/2572) whereas modules are only evaluated once per element
• We are unable to test these functions as them not being modules makes them behave inconsistently in a jasmine environment

To solve this, we need to investigate which of these can be converted into modules completely and the modulise these functions.

[alex-ju]

There are real chances the header-navigation script will be deprecated if the new navigation performs well, which is why it's probably not a priority.

[andysellick]

The modules code was designed to operate on specific chunks of markup, initialised using the data-module attribute. The remaining files listed in this issue don't operate in this way - they either provide library like functions or are depended on by other bits of code. Specifically:

• cookie-functions.js gets initialised and called on every page for the cookie consent mechanism and it wouldn't make sense to tie this to a specific piece of markup
• trigger-event.js is a library function designed mainly to help with testing, but is also called by the analytics and cookies code
• barchart-enhancement is called by govspeak to apply to markup within a govspeak block. While it could be part of the govspeak module it is distinct enough to warrant a separate file
• youtube-link-enhancement is similar to the above

Each of these files has a test file. While it may be possible to initialise some of this code twice, I don't think that converting them to modules is the best approach.