UMD parsers: Make bin/pegjs generate UMD parsers

Part of work on #362.

README.md

@@ -73,10 +73,10 @@ file but with “.js” extension. You can also specify the output file explicit
 
 If you omit both input and output file, standard input and output are used.
 
-By default, the parser object is assigned to `module.exports`, which makes the
-output a Node.js module. You can assign it to another variable by passing a
-variable name using the `-e`/`--export-var` option. This may be helpful if you
-want to use the parser in browser environment.
+The generated parser is in the [UMD](https://github.com/umdjs/umd) format, which
+means it works as a Node.js or AMD module. You can also use the
+`-e`/`--export-var` option to define a global variable into which the parser
+object is assigned to when no module loader is detected.
 
 You can tweak the generated parser with several options:
 

bin/pegjs

@@ -25,9 +25,9 @@ function printHelp() {
   console.log("omitted, standard input and output are used.");
   console.log("");
   console.log("Options:");
-  console.log("  -e, --export-var <variable>        name of the variable where the parser");
-  console.log("                                     object will be stored (default:");
-  console.log("                                     \"module.exports\")");
+  console.log("  -e, --export-var <variable>        name of a global variable into which the");
+  console.log("                                     parser object is assigned to when no module");
+  console.log("                                     loader is detected (default: \"\")");
   console.log("      --cache                        make generated parser cache results");
   console.log("      --allowed-start-rules <rules>  comma-separated list of rules the generated");
   console.log("                                     parser will be allowed to start parsing");
@@ -110,11 +110,11 @@ function readStream(inputStream, callback) {
 
 /* Main */
 
-/* This makes the generated parser a CommonJS module by default. */
-var exportVar = "module.exports";
 var options = {
   cache:     false,
   output:    "source",
+  format:    "umd",
+  exportVar: null,
   optimize:  "speed",
   trace:     false,
   plugins:   []
@@ -128,7 +128,7 @@ while (args.length > 0 && isOption(args[0])) {
       if (args.length === 0) {
         abort("Missing parameter of the -e/--export-var option.");
       }
-      exportVar = args[0];
+      options.exportVar = args[0];
       break;
 
     case "--cache":
@@ -266,9 +266,7 @@ readStream(inputStream, function(input) {
     }
   }
 
-  outputStream.write(
-    exportVar !== "" ? exportVar + " = " + source + ";\n" : source + "\n"
-  );
+  outputStream.write(source);
   if (outputStream !== process.stdout) {
     outputStream.end();
   }