Add upstream

wp-content/plugins/jetpack/modules/widgets/milestone/admin.js

@@ -0,0 +1,31 @@
+( function( $ ) {
+	// We could either be in wp-admin/widgets.php or the customizer.
+	var $container = $( '#customize-controls' );
+
+	if ( ! $container.length ) {
+		$container = $( '#wpbody' );
+	}
+
+	$container.on( 'change', '.milestone-type', function() {
+		var $messageWrapper = $( this )
+			.parent()
+			.find( '.milestone-message-wrapper' );
+
+		$( this )
+			.find( 'input[type="radio"]:checked' )
+			.val() === 'since'
+			? $messageWrapper.hide()
+			: $messageWrapper.show();
+	} );
+
+	function triggerChange() {
+		$container.find( '.milestone-type' ).trigger( 'change' );
+	}
+
+	// Used when adding widget via customizer or saving settings.
+	$( document ).on( 'widget-added widget-updated', function() {
+		triggerChange();
+	} );
+
+	triggerChange();
+} )( jQuery );