diff --git a/.eslintrc.js b/.eslintrc.js
index 2c8a11c26c3..79407c08654 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -116,6 +116,7 @@ module.exports = {
     'sonarjs/no-unused-collection': 'error',
     'sonarjs/no-extra-arguments': 'error',
     'unicorn/no-useless-undefined': 'error',
+    'no-var': 'error',
     // Strict Mode (http://eslint.org/docs/rules/#strict-mode)
     strict: 0,
 
diff --git a/packages/graphiql/resources/renderExample.js b/packages/graphiql/resources/renderExample.js
index 530795cfd24..011cc0dae0f 100644
--- a/packages/graphiql/resources/renderExample.js
+++ b/packages/graphiql/resources/renderExample.js
@@ -13,9 +13,9 @@
  */
 
 // Parse the search string to get url parameters.
-var parameters = {};
+const parameters = {};
 for (const entry of window.location.search.slice(1).split('&')) {
-  var eq = entry.indexOf('=');
+  const eq = entry.indexOf('=');
   if (eq >= 0) {
     parameters[decodeURIComponent(entry.slice(0, eq))] = decodeURIComponent(
       entry.slice(eq + 1),
@@ -49,7 +49,7 @@ function onTabChange(tabsState) {
 }
 
 function updateURL() {
-  var newSearch =
+  const newSearch =
     '?' +
     Object.keys(parameters)
       .filter(function (key) {