CodeMirror: JavaScript mode

+// Demo code (the actual new parser character stream implementation)
+
+function StringStream(string) {
+  this.pos = 0;
+  this.string = string;
+}
+
+StringStream.prototype = {
+  done: function() {return this.pos >= this.string.length;},
+  peek: function() {return this.string.charAt(this.pos);},
+  next: function() {
+    if (this.pos < this.string.length)
+      return this.string.charAt(this.pos++);
+  },
+  eat: function(match) {
+    var ch = this.string.charAt(this.pos);
+    if (typeof match == "string") var ok = ch == match;
+    else var ok = ch && match.test ? match.test(ch) : match(ch);
+    if (ok) {this.pos++; return ch;}
+  },
+  eatWhile: function(match) {
+    var start = this.pos;
+    while (this.eat(match));
+    if (this.pos > start) return this.string.slice(start, this.pos);
+  },
+  backUp: function(n) {this.pos -= n;},
+  column: function() {return this.pos;},
+  eatSpace: function() {
+    var start = this.pos;
+    while (/\s/.test(this.string.charAt(this.pos))) this.pos++;
+    return this.pos - start;
+  },
+  match: function(pattern, consume, caseInsensitive) {
+    if (typeof pattern == "string") {
+      function cased(str) {return caseInsensitive ? str.toLowerCase() : str;}
+      if (cased(this.string).indexOf(cased(pattern), this.pos) == this.pos) {
+        if (consume !== false) this.pos += str.length;
+        return true;
+      }
+    }
+    else {
+      var match = this.string.slice(this.pos).match(pattern);
+      if (match && consume !== false) this.pos += match[0].length;
+      return match;
+    }
+  }
+};
+

JavaScript mode supports a single configuration + option, json, which will set the mode to expect JSON + data rather than a JavaScript program.