Add web workers, parse automatically

I thought the demo might be nicer if it used web workers
to parse the grammar in the background. That way it doesn't
block the DOM, so it's a bit smoother.

Additionally, since we're not blocking the DOM, we can just
automatically re-parse the file as the user types. I set a
debounce of 700ms so that it doesn't fire too frequently. I also
removed the "Parse" button entirely, and set it up so there's a little
"Parsing..." message while it's parsing. I also made to sure to do
a fallback if web workers aren't supported in the browser (and I tested
that it works.

You can try a demo
[here](https://nolanlawson.s3.amazonaws.com/jison/try/index.html).

.gitignore

@@ -4,4 +4,5 @@ node_modules
 # Editor backup files
 *.bak
 *~
-web/content/assets/js/jison.js
+web/content/assets/js/jison.js
+web/crash.log

web/content/assets/js/try.js

@@ -1,5 +1,7 @@
 (function ($) {
 
+var worker = new Worker('../assets/js/worker.js');
+
 var parser,
     parser2;
 
@@ -13,8 +15,20 @@ print = function (){}
 
 var printOut = function (str) { $("#out").html(str); };
 
+function debounce(timeout, fn) {
+    var timer;
+
+    return function() {
+        clearTimeout(timer);
+
+        timer = setTimeout(function() {
+            fn();
+            timer = null;
+        }, timeout);
+    };
+}
+
 $(document).ready(function () {
-    $("#process_btn").click(processGrammar);
     $("#parse_btn").click(runParser);
 
     $("#examples").change(function(ev) {
@@ -23,52 +37,107 @@ $(document).ready(function () {
         $.get("/jison/examples/"+file, function (data) {
                 $("#grammar").val(data);
                 $(document.body).removeClass("loading");
+                processGrammar();
             });
     });
-
+
+    // recompile the grammar using a web worker,
+    // as the user types
+    var onChange = debounce(700, processGrammar);
+    $('#grammar').bind('input propertychange', onChange);
+    processGrammar();
 });
 
 function processGrammar () {
-    var type = "lalr";
-
-    var grammar = $("#grammar").val();
-    try {
-        var cfg = JSON.parse(grammar);
-    } catch(e) {
+
+    function onError(e) {
+        console.log(e);
+        $("#gen_out").html("Oops. Make sure your grammar is " +
+            "in the correct format."+ "\n" + e.stack)
+            .removeClass('good')
+            .removeClass('warning')
+            .addClass('bad');
+    }
+
+    function onSuccess(result) {
+
         try {
-            var cfg = bnf.parse(grammar);
+            parser = Jison.Generator(result.cfg, {type: result.type});
         } catch (e) {
-            $("#gen_out").html("Oops. Make sure your grammar is in the correct format.\n"+e).addClass('bad');
-            return;
+            return onError(e);
+        }
+
+        $("#out").removeClass("good").removeClass("bad").html('');
+        $("#gen_out").removeClass("good").removeClass("bad").removeClass('warning');
+        if (!parser.conflicts) {
+            $("#gen_out").html('Generated successfully!').addClass('good');
+        } else {
+            $("#gen_out").html('Conflicts encountered:<br/>').addClass('bad');
         }
-    }
 
-    Jison.print = function () {};
-    parser = Jison.Generator(cfg, {type: type});
+        $("#download_btn").click(function () {
+                window.location.href = "data:application/javascript;charset=utf-8;base64,"+Base64.encode(parser.generate());
+            }).removeAttr('disabled');
+
+
+
+        parser.resolutions.forEach(function (res) {
+            var r = res[2];
+            if (!r.bydefault) return;
+            $("#gen_out").append(r.msg+"\n"+"("+r.s+", "+r.r+") -> "+r.action);
+        });
+
+        parser2 = parser.createParser();
+    }    
+
+    // for newer browsers
+    function callWorker(grammar) {
+        worker.addEventListener('error', onError);
+        worker.addEventListener('message', function(e) {
+            onSuccess(e.data.result);
+        });
+
+        // ask the web worker to parse the grammar for us    
+        worker.postMessage(grammar);
+    }
+
+    // for older browsers (IE <=9, Android <=4.3)
+    function callNonWorker(grammar) {
+        Jison.print = function () {};
+        var cfg;
 
-    $("#out").removeClass("good").removeClass("bad").html('');
-    $("#gen_out").removeClass("good").removeClass("bad");
-    if (!parser.conflicts) {
-        $("#gen_out").html('Generated successfully!').addClass('good');
+        try {
+            cfg = JSON.parse(grammar);
+        } catch (e) {
+            try { 
+                cfg = bnf.parse(grammar);
+            } catch (e) {
+                return onError(e);
+            }
+        }
+
+        onSuccess({cfg: cfg, type: 'lalr'});
+    }
+
+    $("#gen_out").html("Parsing...")
+      .removeClass('good')
+      .removeClass('bad')
+      .addClass('warning');
+    $('#download_btn').attr('disabled', true);
+
+    var grammar = $("#grammar").val();
+
+    if (typeof Worker !== 'undefined') {
+        callWorker(grammar);
     } else {
-        $("#gen_out").html('Conflicts encountered:<br/>').addClass('bad');
+        callNonWorker(grammar);
     }
-
-    $("#download_btn").click(function () {
-            window.location.href = "data:application/javascript;charset=utf-8;base64,"+Base64.encode(parser.generate());
-        }).removeAttr('disabled');
-
-    parser.resolutions.forEach(function (res) {
-        var r = res[2];
-        if (!r.bydefault) return;
-        $("#gen_out").append(r.msg+"\n"+"("+r.s+", "+r.r+") -> "+r.action);
-    });
-
-    parser2 = parser.createParser();
 }
 
 function runParser () {
-    if (!parser) processGrammar();
+    if (!parser) {
+        processGrammar();
+    }
     printOut("Parsing...");
     var source = $("#source").val();
     try {

web/content/assets/js/worker.js

@@ -0,0 +1,24 @@
+'use strict';
+
+importScripts('jison.js');
+Jison.print = function () {};
+
+// request to parse a grammar
+self.addEventListener('message', function (e) {
+  if (typeof e.data !== 'string') {
+    return;
+  }
+
+  var grammar = e.data;
+
+  var cfg;
+
+  try {
+      cfg = JSON.parse(grammar);
+  } catch (e) {
+      // intentionally throw an error here if it fails to parse
+      cfg = bnf.parse(grammar);
+  }
+
+  self.postMessage({result: {cfg: cfg, type: "lalr"}});
+});

web/content/assets/styles/try.css

@@ -82,3 +82,8 @@ table tr:hover td {
   background: #fee;
   border: 2px solid red;
 }
+
+.warning {
+  background: #feffef;
+  border: 2px solid yellow;
+}

web/content/try.html

@@ -79,7 +79,6 @@ <h2>Describe Your Language</h2>
     ;
 </textarea>
     <p>
-      <button id="process_btn">Generate Parser</button>
       <button id="download_btn" disabled>Download</button>
     </p>
     <pre id="gen_out"></pre>