better typeof symbol transformer

2015-01-15 02:24:32 +11:00
parent 44f06c0b4c
commit b60eca0a76
2 changed files with 14 additions and 2 deletions
--- a/lib/6to5/transformation/transformers/optional-typeof-symbol.js
+++ b/lib/6to5/transformation/transformers/optional-typeof-symbol.js
@@ -3,7 +3,19 @@ var t = require("../../types");
 exports.optional = true;

 exports.UnaryExpression = function (node, parent, file) {
+  this.skip();
+
  if (node.operator === "typeof") {
-    return t.callExpression(file.addHelper("typeof"), [node.argument]);
+    var call = t.callExpression(file.addHelper("typeof"), [node.argument]);
+    if (t.isIdentifier(node.argument)) {
+      var undefLiteral = t.literal("undefined");
+      return t.conditionalExpression(
+        t.binaryExpression("===", t.unaryExpression("typeof", node.argument), undefLiteral),
+        undefLiteral,
+        call
+      );
+    } else {
+      return call;
+    }
  }
 };