Use const in more places

config/jsdoc/api/template/static/scripts/linenumber.js

@@ -1,17 +1,11 @@
 (function() {
-    var counter = 0;
-    var numbered;
-    var source = document.getElementsByClassName('prettyprint source');
-
-    if (source && source[0]) {
-        source = source[0].getElementsByTagName('code')[0];
-
-        numbered = source.innerHTML.split('\n');
-        numbered = numbered.map(function(item) {
-            counter++;
-            return '<span id="line' + counter + '"></span>' + item;
-        });
-
-        source.innerHTML = numbered.join('\n');
+    const source = document.querySelector('.prettyprint.source > code');
+    if (source) {
+        source.innerHTML = source.innerHTML
+            .split('\n')
+            .map(function (item, i) {
+                return '<span id="line' + (i + 1) + '"></span>' + item;
+            })
+            .join('\n');
     }
 })();