[javascript mode] Fix indentation after trailing-comma array

Closes #2753

Author: marijnh

mode/javascript/javascript.js

@@ -590,7 +590,7 @@ CodeMirror.defineMode("javascript", function(config, parserConfig) {
   }
   function maybeArrayComprehension(type) {
     if (type == "for") return pass(comprehension, expect("]"));
-    if (type == ",") return cont(commasep(expressionNoComma, "]"));
+    if (type == ",") return cont(commasep(maybeexpressionNoComma, "]"));
     return pass(commasep(expressionNoComma, "]"));
   }
   function comprehension(type) {

mode/javascript/test.js

@@ -147,6 +147,13 @@
   MT("scary_regexp",
      "[string-2 /foo[[/]]bar/];");
 
+  MT("indent_strange_array",
+     "[keyword var] [variable x] [operator =] [[",
+     "  [number 1],,",
+     "  [number 2],",
+     "]];",
+     "[number 10];");
+
   var jsonld_mode = CodeMirror.getMode(
     {indentUnit: 2},
     {name: "javascript", jsonld: true}