Refactor component JavaScript and add tests

[tomdoughty]

Description

Refactor the component JavaScript to use modern ES6 syntax with new JavaScript coding standards for NHS.UK frontend.

Draft of a custom written details polyfill including toggle class and attribute utils I have separated into their own files.

The exisiting polyfill was overkill for our browser support which caused complications for SPAs. I will be adding unit tests for this as part of the ES6 refactor but thought it is worth creating this PR for discussion. Done this way it is a non breaking change so could be merged if we decide it is better.

Update to the latest version of GOV.UK autocomplete

Related issues

#450 #408 #545

Checklist

• Tested against our testing policy (Resolution, Browser & Accessibility)
• Follows our coding standards and style guide
• CHANGELOG entry

[chrimesdev]

Hey @tomdoughty this looks really good. Do you think we could include it in the release 3.0.0? Would be good to have the breaking changes all go out together rather than do another one in a month or so. We are putting 3.0.0 changes on the develop branch if you want to rebase with that.

We're going to be removing the feedback banner, so any JavaScript relating to that could be deleted.

[chrimesdev]

These are mainly reminders for myself so I don’t forget, but stuff we could look at:

• Update the any documentation or examples for importing JavaScript, as the import names have changed eg. nhsuk_header(); to Header(); eg. https://github.com/nhsuk/nhsuk-frontend/blob/master/docs/installation/installing-with-npm.md#option-2-import-javascript-using-modules
• Can we import and initialise details.polyfill.js the same way we do other components for consistency. eg import Details from './components/details/details.polyfill'; Details();
• Do we still need to use document.addEventListener('DOMContentLoaded', () => { when initialising the components JavaScript
• Test the compiled JavaScript (nhsuk.min.js) in a separate app that uses compiled files to consume the FE library
• Will need a change log entry for the breaking change and how to update applications

Can be done at a later date:

• Add documentation to the contributing guidelines for Jest tests, prehooks and JavaScript coding standards

This pull request also potentially fixes #450 & #408 & #545

[chrimesdev]

Just need to do some final testing with the JS (in a package and compiled versions) and add a change log entry then this will be good to go in release 3.0.0 🍾

[chrimesdev]

The compiled JavaScript seems to be working fine.

[chrimesdev]

Will work on the changelog on develop

[chrimesdev]

Thanks @tomdoughty 🍾 🔥