[javascript mode] Also fix computed property TS syntax for type exprs and classes

Issue codemirror#5909

Author: marijnh

mode/javascript/javascript.js

@@ -621,7 +621,7 @@ CodeMirror.defineMode("javascript", function(config, parserConfig) {
     } else if (type == ":") {
       return cont(typeexpr)
     } else if (type == "[") {
-      return cont(expect("variable"), maybetype, expect("]"), typeprop)
+      return cont(expect("variable"), maybetypeOrIn, expect("]"), typeprop)
     } else if (type == "(") {
       return pass(functiondecl, typeprop)
     }
@@ -754,7 +754,7 @@ CodeMirror.defineMode("javascript", function(config, parserConfig) {
     }
     if (type == "number" || type == "string") return cont(isTS ? classfield : functiondef, classBody);
     if (type == "[")
-      return cont(expression, maybetype, expect("]"), isTS ? classfield : functiondef, classBody)
+      return cont(expression, maybetypeOrIn, expect("]"), isTS ? classfield : functiondef, classBody)
     if (value == "*") {
       cx.marked = "keyword";
       return cont(classBody);