Found a neater trick how to defend against |undefined| redefinition

lib/compiler.js

@@ -1,6 +1,6 @@
 /* PEG.js compiler. */
 
-(function() {
+(function(undefined) {
 
 /* ===== PEG ===== */
 
@@ -39,7 +39,7 @@ PEG.GrammarError.prototype = Error.prototype;
 PEG.ArrayUtils = {
   /* Like Python's |range|, but without |step|. */
   range: function(start, stop) {
-    if (typeof(stop) === "undefined") {
+    if (stop === undefined) {
       stop = start;
       start = 0;
     }
@@ -193,11 +193,11 @@ PEG.Compiler = {
           /\$\{([a-zA-Z_][a-zA-Z0-9_]*)(\|([a-zA-Z_][a-zA-Z0-9_]*))?\}/g,
           function(match, name, dummy, filter) {
             var value = vars[name];
-            if (typeof(value) === "undefined") {
+            if (value === undefined) {
               throw new Error("Undefined variable: \"" + name + "\".");
             }
 
-            if (typeof(filter) !== "undefined" && filter != "") { // JavaScript engines differ here.
+            if (filter !== undefined && filter != "") { // JavaScript engines differ here.
               if (filter === "string") {
                 return PEG.StringUtils.quote(value);
               } else {
@@ -297,7 +297,7 @@ PEG.Compiler = {
 
         rule_ref:
           function(node) {
-            if (typeof(ast.rules[node.name]) === "undefined") {
+            if (ast.rules[node.name] === undefined) {
               throw new PEG.GrammarError(
                 "Referenced rule \"" + node.name + "\" does not exist."
               );