diff --git a/js/legacy/markdown-it-checkbox.js b/js/legacy/markdown-it-checkbox.js
index 3f195748d..74406a091 100644
--- a/js/legacy/markdown-it-checkbox.js
+++ b/js/legacy/markdown-it-checkbox.js
@@ -1,6 +1,4 @@
-var _, checkboxReplace;
-
-_ = require('underscore');
+var checkboxReplace;
 
 checkboxReplace = function(md, options, Token) {
   "use strict";
@@ -12,7 +10,7 @@ checkboxReplace = function(md, options, Token) {
     divClass: 'checkbox',
     idPrefix: 'checkbox'
   };
-  options = _.extend(defaults, options);
+  options = Object.assign(defaults, options);
   pattern = /\[(X|\s|\_|\-)\]\s(.*)/i;
   createTokens = function(checked, label, Token) {
     var id, idNumeric, nodes, token;