WordPress
diff --git a/‎src/wp-includes/js-interop.php‎
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diff --git a/‎src/wp-includes/script-loader.php‎
Lines changed: 150 additions & 0 deletions b/‎src/wp-includes/script-loader.php‎
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@@ -3464,3 +3464,153 @@ function wp_remove_surrounding_empty_script_tags( $contents ) {
 		);
 	}
 }
+
+/**
+ * Return the corresponding JavaScript `dataset` name for an attribute
+ * if it represents a custom data attribute, or `null` if not.
+ *
+ * Custom data attributes appear in an element's `dataset` property in a
+ * browser, but there's a specific way the names are translated from HTML
+ * into JavaScript. This function indicates how the name would appear in
+ * JavaScript if a browser would recognize it as a custom data attribute.
+ *
+ * Example:
+ *
+ *     // Dash-letter pairs turn into capital letters.
+ *     'postId'       === wp_js_dataset_name( 'data-post-id' );
+ *     'Before'       === wp_js_dataset_name( 'data--before' );
+ *     '-One--Two---' === wp_js_dataset_name( 'data---one---two---' );
+ *
+ *     // Not every attribute name will be interpreted as a custom data attribute.
+ *     null === wp_js_dataset_name( 'post-id' );
+ *     null === wp_js_dataset_name( 'data' );
+ *
+ *     // Some very surprising names will; for example, a property whose name is the empty string.
+ *     '' === wp_js_dataset_name( 'data-' );
+ *     0  === strlen( wp_js_dataset_name( 'data-' ) );
+ *
+ * @since 6.9.0
+ *
+ * @see https://html.spec.whatwg.org/#concept-domstringmap-pairs
+ * @see wp_html_custom_data_attribute_name()
+ *
+ * @param string $html_attribute_name Raw attribute name as found in the source HTML.
+ * @return string|null Transformed `dataset` name, if interpretable as a custom data attribute, else `null`.
+ */
+function wp_js_dataset_name( string $html_attribute_name ): ?string {
+	if ( 0 !== substr_compare( $html_attribute_name, 'data-', 0, 5, true ) ) {
+		return null;
+	}
+
+	$end = strlen( $html_attribute_name );
+
+	/*
+	 * If it contains characters which would end the attribute name parsing then
+	 * something else is wrong and this contains more than just an attribute name.
+	 */
+	if ( ( $end - 5 ) !== strcspn( $html_attribute_name, "=/> \t\f\r\n", 5 ) ) {
+		return null;
+	}
+
+	/*
+	 * > For each name in list, for each U+002D HYPHEN-MINUS character (-)
+	 * > in the name that is followed by an ASCII lower alpha, remove the
+	 * > U+002D HYPHEN-MINUS character (-) and replace the character that
+	 * > followed it by the same character converted to ASCII uppercase.
+	 *
+	 * @link https://html.spec.whatwg.org/#concept-domstringmap-pairs
+	 */
+	$custom_name = '';
+	$at          = 5;
+	$was_at      = $at;
+
+	while ( $at < $end ) {
+		$next_dash_at = strpos( $html_attribute_name, '-', $at );
+		if ( false === $next_dash_at || $next_dash_at === $end - 1 ) {
+			break;
+		}
+
+		// Transform `-a` to `A`, for example.
+		$c = $html_attribute_name[ $next_dash_at + 1 ];
+		if ( ( $c >= 'A' && $c <= 'Z' ) || ( $c >= 'a' && $c <= 'z' ) ) {
+			$prefix       = substr( $html_attribute_name, $was_at, $next_dash_at - $was_at );
+			$custom_name .= strtolower( $prefix );
+			$custom_name .= strtoupper( $c );
+			$at           = $next_dash_at + 2;
+			$was_at       = $at;
+			continue;
+		}
+
+		$at = $next_dash_at + 1;
+	}
+
+	// If nothing has been added it means there are no dash-letter pairs; return the name as-is.
+	return '' === $custom_name
+		? strtolower( substr( $html_attribute_name, 5 ) )
+		: ( $custom_name . strtolower( substr( $html_attribute_name, $was_at ) ) );
+}
+
+/**
+ * Returns a corresponding HTML attribute name for the given name,
+ * if that name were found in a JS element’s `dataset` property.
+ *
+ * Example:
+ *
+ *     'data-post-id'        === wp_html_custom_data_attribute_name( 'postId' );
+ *     'data--before'        === wp_html_custom_data_attribute_name( 'Before' );
+ *     'data---one---two---' === wp_html_custom_data_attribute_name( '-One--Two---' );
+ *
+ *     // Not every attribute name will be interpreted as a custom data attribute.
+ *     null === wp_html_custom_data_attribute_name( '/not-an-attribute/' );
+ *     null === wp_html_custom_data_attribute_name( 'no spaces' );
+ *
+ *     // Some very surprising names will; for example, a property whose name is the empty string.
+ *     'data-' === wp_html_custom_data_attribute_name( '' );
+ *
+ * @since 6.9.0
+ *
+ * @see https://html.spec.whatwg.org/#concept-domstringmap-pairs
+ * @see wp_js_dataset_name()
+ *
+ * @param string $js_dataset_name Name of JS `dataset` property to transform.
+ * @return string|null Corresponding name of an HTML custom data attribute for the given dataset name,
+ *                     if possible to represent in HTML, otherwise `null`.
+ */
+function wp_html_custom_data_attribute_name( string $js_dataset_name ): ?string {
+	$end = strlen( $js_dataset_name );
+	if ( 0 === $end ) {
+		return 'data-';
+	}
+
+	/*
+	 * If it contains characters which would end the attribute name parsing then
+	 * something it’s not possible to represent this in HTML.
+	 */
+	if ( strcspn( $js_dataset_name, "=/> \t\f\r\n" ) !== $end ) {
+		return null;
+	}
+
+	$html_name = 'data-';
+	$at        = 0;
+	$was_at    = $at;
+
+	while ( $at < $end ) {
+		$next_upper_after = strcspn( $js_dataset_name, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', $at );
+		$next_upper_at    = $at + $next_upper_after;
+		if ( $next_upper_at >= $end ) {
+			break;
+		}
+
+		$prefix     = substr( $js_dataset_name, $was_at, $next_upper_at - $was_at );
+		$html_name .= strtolower( $prefix );
+		$html_name .= '-' . strtolower( $js_dataset_name[ $next_upper_at ] );
+		$at         = $next_upper_at + 1;
+		$was_at     = $at;
+	}
+
+	if ( $was_at < $end ) {
+		$html_name .= strtolower( substr( $js_dataset_name, $was_at ) );
+	}
+
+	return $html_name;
+}