Lodash: Refactor away from _.countBy() (#42231)

* Editor: Remove _.flatMap() from DocumentOutline

* Lodash: Refactor both countBy usages

* Editor: Remove _.get() from DocumentOutline

* ESLint: Deprecate countBy

* Use .flatMap()

.eslintrc.js

@@ -82,6 +82,7 @@ module.exports = {
 							'chunk',
 							'clamp',
 							'concat',
+							'countBy',
 							'defaults',
 							'defaultTo',
 							'differenceWith',

bin/plugin/commands/changelog.js

@@ -2,7 +2,6 @@
  * External dependencies
  */
 const {
-	countBy,
 	groupBy,
 	escapeRegExp,
 	uniq,
@@ -309,7 +308,17 @@ function getIssueFeature( issue ) {
 	// 1. Prefer explicit mapping of label to feature.
 	if ( featureCandidates.length ) {
 		// Get occurances of the feature labels.
-		const featureCounts = countBy( featureCandidates );
+		const featureCounts = featureCandidates.reduce(
+			/**
+			 * @param {Record<string,number>} acc     Accumulator
+			 * @param {string}                feature Feature label
+			 */
+			( acc, feature ) => ( {
+				...acc,
+				[ feature ]: ( acc[ feature ] || 0 ) + 1,
+			} ),
+			{}
+		);
 
 		// Check which matching label occurs most often.
 		const rankedFeatures = Object.keys( featureCounts ).sort(

packages/editor/src/components/document-outline/index.js

@@ -1,8 +1,3 @@
-/**
- * External dependencies
- */
-import { countBy, flatMap, get } from 'lodash';
-
 /**
  * WordPress dependencies
  */
@@ -50,7 +45,7 @@ const multipleH1Headings = [
  * @return {Array} An array of heading blocks enhanced with the properties described above.
  */
 const computeOutlineHeadings = ( blocks = [] ) => {
-	return flatMap( blocks, ( block = {} ) => {
+	return blocks.flatMap( ( block = {} ) => {
 		if ( block.name === 'core/heading' ) {
 			return {
 				...block,
@@ -83,7 +78,13 @@ export const DocumentOutline = ( {
 	// Not great but it's the simplest way to locate the title right now.
 	const titleNode = document.querySelector( '.editor-post-title__input' );
 	const hasTitle = isTitleSupported && title && titleNode;
-	const countByLevel = countBy( headings, 'level' );
+	const countByLevel = headings.reduce(
+		( acc, heading ) => ( {
+			...acc,
+			[ heading.level ]: ( acc[ heading.level ] || 0 ) + 1,
+		} ),
+		{}
+	);
 	const hasMultipleH1 = countByLevel[ 1 ] > 1;
 
 	return (
@@ -155,7 +156,7 @@ export default compose(
 		return {
 			title: getEditedPostAttribute( 'title' ),
 			blocks: getBlocks(),
-			isTitleSupported: get( postType, [ 'supports', 'title' ], false ),
+			isTitleSupported: postType?.supports?.title ?? false,
 		};
 	} )
 )( DocumentOutline );