refactor(transpiler): instanceof

Author: vojtajina

tools/transpiler/src/codegeneration/InstanceOfTransformer.js

@@ -1,6 +1,9 @@
 import {INSTANCEOF} from 'traceur/src/syntax/TokenType';
-
 import {ParseTreeTransformer} from './ParseTreeTransformer';
+import {
+  createBinaryExpression,
+  createOperatorToken
+} from 'traceur/src/codegeneration/ParseTreeFactory';
 
 /**
  * Transforms `a instanceof b` to `a is b`,
@@ -11,15 +14,12 @@ export class InstanceOfTransformer extends ParseTreeTransformer {
    * @return {ParseTree}
    */
   transformBinaryExpression(tree) {
-    tree.left = this.transformAny(tree.left);
-    tree.right = this.transformAny(tree.right);
+    tree = super(tree);
 
-    if (tree.operator.type === 'instanceof') {
-      // TODO(vojta): do this in a cleaner way.
-      tree.operator.type = 'is';
-      return tree;
+    if (tree.operator.type === INSTANCEOF) {
+      return createBinaryExpression(tree.left, createOperatorToken('is'), tree.right);
     }
 
     return tree;
   }
-}
+}