i18n-calypso: Replace EventEmitter with simplified subscriber callbacks

[aduth]

Proposed Changes

• Removes EventEmitter usage from i18n-calypso package, substituting a simplified subscriber implementation

Why are these changes being made?

• Move away from outdated EventEmitter data approach toward conventions more conventional and compatible with React (e.g. useEffect subscribers)
• Reduce bundle size by eliminating events package in common dependency (estimated 2kb gzipped)
• Likely performance improvement due to lack of overhead of event emitter; we're not handling multiple event types, or forwarding parameters, or handling errors.

On performance, I discovered that the events library does have a surprisingly-performant subscriber removal behavior. Early iterations here included a "readable" Array#filter implementation (see a8fb2d4), but considering that many of our localized components will remove event listeners once they're unmounted, it seemed worthwhile to micro-optimize. After several rounds of micro-benchmarking, I found a solution which performs even better (~38%) than events's implementation, and ~850x better than a naive Array#filter implementation in a scenario with 2000 subscribers.

Separately, I had explored an implementation which largely maintained the same API if we'd rather reduce the scope of the changes.

Testing Instructions

• The idea is that this should be drop-in compatible for localization, and should have no impact on the display and re-rendering of translation data. Changes can be emulated by switching languages in the dashboard.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-143672

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-143672&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-143672&env=a8c-for-agencies

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• blaze-dashboard
• command-palette-wp-admin
• happy-blocks
• help-center
• notifications
• odyssey-stats
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug remove/i18n-events-dep on your sandbox.

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~134 bytes removed 📉 [gzipped])

name                   parsed_size           gzip_size
entry-subscriptions         -280 B  (-0.0%)      -85 B  (-0.0%)
entry-login                 -280 B  (-0.0%)      -82 B  (-0.0%)
entry-main                  -260 B  (-0.0%)      -68 B  (-0.0%)
entry-reauth-required       -258 B  (-0.0%)      -65 B  (-0.0%)
entry-stepper               -219 B  (-0.0%)      -53 B  (-0.0%)
entry-domains-landing       -174 B  (-0.0%)      -15 B  (-0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Sections (~241 bytes removed 📉 [gzipped])

name                                parsed_size           gzip_size
stepper-user-step                         -61 B  (-0.0%)      -28 B  (-0.0%)
async-step-use-my-domain                  -61 B  (-0.0%)      -31 B  (-0.0%)
async-step-unified-plans                  -61 B  (-0.0%)      -27 B  (-0.0%)
async-step-unified-domains                -61 B  (-0.0%)      -28 B  (-0.0%)
site-migration-flow                       -41 B  (-0.1%)      -20 B  (-0.1%)
woocommerce-installation                  -20 B  (-0.0%)      -15 B  (-0.0%)
woocommerce                               -20 B  (-0.0%)      -15 B  (-0.0%)
themes                                    -20 B  (-0.0%)      -15 B  (-0.0%)
theme                                     -20 B  (-0.0%)      -15 B  (-0.0%)
subscribers                               -20 B  (-0.0%)      -15 B  (-0.0%)
stats                                     -20 B  (-0.0%)      -15 B  (-0.0%)
staging-site                              -20 B  (-0.0%)      -13 B  (-0.0%)
sites-dashboard                           -20 B  (-0.0%)      -13 B  (-0.0%)
site-settings                             -20 B  (-0.0%)      -13 B  (-0.0%)
site-purchases                            -20 B  (-0.0%)      -10 B  (-0.0%)
site-profiler                             -20 B  (-0.0%)      -15 B  (-0.0%)
site-performance                          -20 B  (-0.0%)      -13 B  (-0.0%)
site-monitoring                           -20 B  (-0.0%)      -13 B  (-0.0%)
site-logs                                 -20 B  (-0.0%)      -13 B  (-0.0%)
site-blocks                               -20 B  (-0.0%)      -15 B  (-0.0%)
settings-writing                          -20 B  (-0.0%)      -15 B  (-0.0%)
settings-security                         -20 B  (-0.0%)      -15 B  (-0.0%)
settings-reading                          -20 B  (-0.0%)      -15 B  (-0.0%)
settings-podcast                          -20 B  (-0.0%)      -15 B  (-0.0%)
settings-performance                      -20 B  (-0.0%)      -15 B  (-0.0%)
settings-newsletter                       -20 B  (-0.0%)      -15 B  (-0.0%)
settings-jetpack                          -20 B  (-0.0%)      -15 B  (-0.0%)
settings-discussion                       -20 B  (-0.0%)      -15 B  (-0.0%)
settings                                  -20 B  (-0.0%)      -15 B  (-0.0%)
security                                  -20 B  (-0.0%)      -15 B  (-0.0%)
scan                                      -20 B  (-0.0%)      -15 B  (-0.0%)
reader                                    -20 B  (-0.0%)      -14 B  (-0.0%)
purchases                                 -20 B  (-0.0%)      -10 B  (-0.0%)
purchase-product                          -20 B  (-0.0%)      -15 B  (-0.0%)
promote-post-i2                           -20 B  (-0.0%)      -15 B  (-0.0%)
privacy                                   -20 B  (-0.0%)      -15 B  (-0.0%)
posts-custom                              -20 B  (-0.0%)      -15 B  (-0.0%)
posts                                     -20 B  (-0.0%)      -15 B  (-0.0%)
plugins                                   -20 B  (-0.0%)      -13 B  (-0.0%)
plans                                     -20 B  (-0.0%)      -13 B  (-0.0%)
performance-profiler                      -20 B  (-0.0%)      -15 B  (-0.0%)
people                                    -20 B  (-0.0%)      -15 B  (-0.0%)
patterns                                  -20 B  (-0.0%)      -13 B  (-0.0%)
pages                                     -20 B  (-0.0%)      -15 B  (-0.0%)
overview                                  -20 B  (-0.0%)      -13 B  (-0.0%)
notification-settings                     -20 B  (-0.0%)      -15 B  (-0.0%)
migrate                                   -20 B  (-0.0%)      -15 B  (-0.0%)
media                                     -20 B  (-0.0%)      -15 B  (-0.0%)
me                                        -20 B  (-0.0%)      -15 B  (-0.0%)
marketplace                               -20 B  (-0.0%)      -15 B  (-0.0%)
marketing                                 -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-social                            -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-search                            -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-connect                           -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-settings                    -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-pricing                     -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-plugin-management           -20 B  (-0.0%)      -13 B  (-0.0%)
jetpack-cloud-partner-portal              -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-overview                    -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-manage-pricing              -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-features-comparison         -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud-agency-signup               -20 B  (-0.0%)      -15 B  (-0.1%)
jetpack-cloud-agency-dashboard            -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-cloud                             -20 B  (-0.0%)      -15 B  (-0.0%)
jetpack-app                               -20 B  (-0.0%)      -15 B  (-0.0%)
import                                    -20 B  (-0.0%)      -15 B  (-0.0%)
hosting                                   -20 B  (-0.0%)      -13 B  (-0.0%)
home                                      -20 B  (-0.0%)      -15 B  (-0.0%)
help                                      -20 B  (-0.0%)      -15 B  (-0.0%)
gutenberg-editor                          -20 B  (-0.0%)      -15 B  (-0.0%)
google-my-business                        -20 B  (-0.0%)      -15 B  (-0.0%)
github-deployments                        -20 B  (-0.0%)      -13 B  (-0.0%)
export                                    -20 B  (-0.0%)      -15 B  (-0.0%)
entrepreneur-flow                         -20 B  (-0.0%)      -15 B  (-0.0%)
email                                     -20 B  (-0.0%)      -15 B  (-0.0%)
earn                                      -20 B  (-0.0%)      -15 B  (-0.0%)
domains                                   -20 B  (-0.0%)      -13 B  (-0.0%)
developer                                 -20 B  (-0.0%)      -15 B  (-0.0%)
customize                                 -20 B  (-0.0%)      -15 B  (-0.0%)
concierge                                 -20 B  (-0.0%)      -15 B  (-0.0%)
comments                                  -20 B  (-0.0%)      -15 B  (-0.0%)
checkout                                  -20 B  (-0.0%)      -15 B  (-0.0%)
backup                                    -20 B  (-0.0%)      -15 B  (-0.0%)
add-ons                                   -20 B  (-0.0%)      -15 B  (-0.0%)
activity                                  -20 B  (-0.0%)      -15 B  (-0.0%)
account-close                             -20 B  (-0.0%)      -15 B  (-0.0%)
account                                   -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-woopayments              -20 B  (-0.0%)      -16 B  (-0.0%)
a8c-for-agencies-team                     -20 B  (-0.0%)      -14 B  (-0.0%)
a8c-for-agencies-sites                    -20 B  (-0.0%)      -11 B  (-0.0%)
a8c-for-agencies-settings                 -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-referrals                -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-purchases                -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-plugins                  -20 B  (-0.0%)      -13 B  (-0.0%)
a8c-for-agencies-partner-directory        -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-overview                 -20 B  (-0.0%)      -11 B  (-0.0%)
a8c-for-agencies-migrations               -20 B  (-0.0%)      -17 B  (-0.0%)
a8c-for-agencies-marketplace              -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-landing                  -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies-client                   -20 B  (-0.0%)      -14 B  (-0.0%)
a8c-for-agencies-agency-tier              -20 B  (-0.0%)      -15 B  (-0.0%)
a8c-for-agencies                          -20 B  (-0.0%)      -15 B  (-0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Async-loaded Components (~51 bytes removed 📉 [gzipped])

name                                                                              parsed_size           gzip_size
async-load-automattic-help-center-stepper                                               -61 B  (-0.0%)      -32 B  (-0.0%)
async-load-signup-steps-woocommerce-install-transfer                                    -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-woocommerce-install-step-store-address                          -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-woocommerce-install-step-business-info                          -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-woocommerce-install-confirm                                     -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-website-content-section-types                                   -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-website-content                                                 -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-user                                                            -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-store-features                                                  -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-starting-point                                                  -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-social-profiles                                                 -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-site-picker                                                     -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-site-or-domain                                                  -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-site-options                                                    -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-site                                                            -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-rewind-were-backing                                             -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-rewind-form-creds                                               -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-plans-theme-preselected                                         -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-plans                                                           -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-page-picker                                                     -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-new-or-existing-site                                            -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-intent                                                          -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-hosting-decider                                                 -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-emails                                                          -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-domains                                                         -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-difm-site-picker                                                -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-design-picker                                                   -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-creds-permission                                                -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-creds-confirm                                                   -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-courses                                                         -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-clone-start                                                     -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-clone-ready                                                     -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-clone-point                                                     -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-clone-destination                                               -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-signup-steps-clone-credentials                                               -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-signup-steps-clone-cloning                                                   -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-purchase-modal-wrapper                                                       -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-my-sites-checkout-purchase-modal-is-eligible-for-one-click-checkou...        -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-masterbar-cart-masterbar-cart-wrapper                                        -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-design-playground                                                            -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-design-blocks                                                                -20 B  (-0.0%)      -10 B  (-0.0%)
async-load-design                                                                       -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-calypso-notifications                                                        -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-calypso-blocks-support-article-dialog-dialog                                 -20 B  (-0.0%)      -16 B  (-0.0%)
async-load-calypso-blocks-jitm-templates-home-task                                      -20 B  (-0.0%)      -15 B  (-0.1%)
async-load-automattic-help-center                                                       -20 B  (-0.0%)      -15 B  (-0.0%)
async-load-calypso-layout-community-translator                                          +11 B  (+0.0%)       +7 B  (+0.1%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.