Add to changelog

CHANGELOG.md

@@ -12,6 +12,19 @@ We've deprecated the `govuk-header__link--service-name` class, and will remove i
 
 This change was introduced in [pull request #2617: Do not make the service name in the header a link if no `serviceUrl` is provided](https://github.com/alphagov/govuk-frontend/pull/2617).
 
+#### File extensions added for JavaScript ES Module imports
+In 4.1.0, we started providing our component JavaScript in ES module format. This JavaScript used import statements without [mandatory file extensions](https://nodejs.org/api/esm.html#mandatory-file-extensions), as required by Node.js.
+
+We have now updated our component JavaScript to include these missing file extensions. If you previously received an error similar to the below, this fix should resolve that issue:
+
+```
+Cannot find module '../node_modules/govuk-frontend/govuk-esm/common' imported from ../node_modules/govuk-frontend/govuk-esm/all.mjs
+```
+
+If you are already successfully importing our JavaScript as ES modules, you should not need to make any changes, but there may be config you can remove. For example, removing `fullySpecified: false` from your Webpack config file.
+
+This change was introduced in [pull request #2658: Add missing mandatory file extensions for ESM JavaScript](https://github.com/alphagov/govuk-frontend/pull/2658)
+
 ### Fixes
 
 We’ve made fixes to GOV.UK Frontend in the following pull requests: