README

Polyfills for WordPress Core packages not yet available or complete in older WordPress versions.

This package conditionally registers @wordpress/* packages as both classic scripts (IIFE) and script modules (ESM) when they are not already provided by Core or Gutenberg. It is intended to be used while Jetpack supports WordPress versions whose bundled packages are missing or incomplete. Revisit this package once Jetpack's minimum supported WordPress version reaches 7.1.

Problem

WordPress 7.0 introduces several new packages (@wordpress/boot, @wordpress/route, @wordpress/theme, etc.) that plugins built with @wordpress/build depend on. On older WordPress versions, these packages are missing or ship incomplete implementations — for example, wp-private-apis has an allowlist that rejects @wordpress/theme, @wordpress/route, and newer dashboard packages, and wp-notices lacks component exports that @wordpress/boot requires.

This package provides those missing or updated packages so that plugins using @wordpress/build can work across Jetpack's supported WordPress versions.

What it polyfills

Classic scripts (IIFE)

Handle	Source package	Force-replaced?
`wp-notices`	`@wordpress/notices`	Yes on WP < 7.0 — missing component exports
`wp-private-apis`	`@wordpress/private-apis`	Yes on WP < 7.1 unless Gutenberg >= 23.5.0 is active — incomplete allowlist
`wp-theme`	`@wordpress/theme`	No — only registered if absent
`wp-views`	`@wordpress/views`	No — only registered if absent

Script modules (ESM)

Module ID	Source package
`@wordpress/boot`	`@wordpress/boot`
`@wordpress/route`	`@wordpress/route`
`@wordpress/a11y`	`@wordpress/a11y`

Script modules use "first-wins" semantics — if Core or Gutenberg already registered the module, the polyfill is silently ignored.

How it works

WP_Build_Polyfills::register() hooks into wp_default_scripts at priority 20, after Core (priority 0) and Gutenberg (priority 10) have registered their scripts.
For each polyfill, it checks whether a built asset file exists (build/scripts/*/index.asset.php or build/modules/*/index.asset.php).
For classic scripts, it checks whether the handle is already registered. Scripts marked for force replacement are deregistered and re-registered with the polyfill version when the WordPress version is below the script's threshold and active Gutenberg is not known to provide a compatible implementation. Non-force scripts are skipped if already registered.
For script modules, it calls wp_register_script_module(), which silently ignores duplicates.

wp-private-apis has an additional Gutenberg-version guard because the dashboard packages require a private-apis allowlist that includes @wordpress/widget-dashboard. Gutenberg 23.4.0 and older do not include that allowlist entry; Gutenberg 23.5.0 is expected to be the first active-Gutenberg version that matches the current @next package build used here.

Usage

Call register() early in your plugin, specifying a consumer name and the polyfills you need:

use Automattic\Jetpack\WP_Build_Polyfills\WP_Build_Polyfills;

WP_Build_Polyfills::register( 'my-plugin', array(
    'wp-notices',
    'wp-private-apis',
    '@wordpress/boot',
    '@wordpress/route',
) );

Available handles are listed in WP_Build_Polyfills::SCRIPT_HANDLES and WP_Build_Polyfills::MODULE_IDS.

Multiple plugins can call register() — the hook is only added once, and all requested polyfills are merged. You can inspect which consumers requested which polyfills via WP_Build_Polyfills::get_consumers().

The version threshold for force-replacements can be overridden with a third parameter:

WP_Build_Polyfills::register( 'my-plugin', array( 'wp-notices' ), '7.1' );

Boot module asset file

Packages that use @wordpress/build to generate pages get a hardcoded reference to build/modules/boot/index.min.asset.php in the generated page templates. This file provides the classic script dependencies and version hash needed to bootstrap the page.

When @wordpress/build stops bundling the boot module (as planned in upcoming Gutenberg changes), this asset file will no longer be generated. This package builds its own boot module asset file, and ships a bin script (provide-boot-asset-file) that copies it to the expected location in the consumer's build directory.

Consuming packages should add @automattic/jetpack-wp-build-polyfills as a devDependency and call the script after wp-build:

"build:boot-proxy": "provide-boot-asset-file"

Development

# Build polyfills (development)
pnpm run build

# Build polyfills (production)
pnpm run build-production

# Run PHP tests
composer run test-php

automattic / jetpack-wp-build-polyfills

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