Use event delegation

[bronzehedwick]

Description

Instead of attaching a new root-level event listener for bubbling events
for every choices instance, use a simple event delegation script to
handle each event type.

Each event callback function already is coded as if it were fully
delegated, since the events are attached at the document level, so
no changes are needed to detect which element is being called.

Note that focus and blur event do not bubble, so they have been left as
they are.

Also note that the event delegation uses an IIFE purposely instead of ES6 modules, since the event list should be globally cached, and it doesn't make sense to instantiate a new scope for each instance (then we're back where we started!)

Motivation and Context

Using event delegation increase page speed, especially if there are many choices instances.

fix #643

How Has This Been Tested?

I ran the standard tests via npm test on macOS 10.13.6.

I also tested the local server manually to make sure I could still perform all operations.

This change's scope is limited to adding an event delegation script and the _addEventListeners and _removeEventListeners functions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[bronzehedwick]

The tests are failing for this PR, but it's because cypress fails to start. I can't think of any code changes here that would cause that. And funny enough I'm seeing a similar issue with cypress failing to start for a work project. Is there some larger issue with cypress going on?

Here's the relevant log output.

[22:15:14]  Verifying Cypress can run /home/travis/.cache/Cypress/3.1.5/Cypress [started]

[nodemon] 1.18.10

[nodemon] to restart at any time, enter `rs`

[nodemon] watching: *.*

[nodemon] starting `npm run css:build`

[22:15:15]  Verifying Cypress can run /home/travis/.cache/Cypress/3.1.5/Cypress [failed]

Cypress failed to start.

EDIT

This same issue is happening on several other PRs in this repo as well.

• ADA accessibility label fixes #642
• Fix first option if disabled (#473) #583
• Fix types on Templates interface function signatures #619

[jshjohnson]

If you merge in latest master, the CI build should be fixed 👍

[guidefreitas]

This PR attenuate some of performance issues we are having when a select has a lot of options.

Thanks!

[bronzehedwick]

If you merge in latest master, the CI build should be fixed 👍

I merged in master and the builds now pass. Thanks!

[bronzehedwick]

@jshjohnson any chance this PR can get a review? Thanks!

[jshjohnson]

Thanks @bronzehedwick 👍

[markx3]

Awesome! 🎉

[jshjohnson]

This fix is included in version 7.0.2 👍