[javascript mode] Simplify number tokenizing and add support for n prefix

Issue codemirror#5411

Author: marijnh

mode/javascript/javascript.js

@@ -75,17 +75,10 @@ CodeMirror.defineMode("javascript", function(config, parserConfig) {
       return ret(ch);
     } else if (ch == "=" && stream.eat(">")) {
       return ret("=>", "operator");
-    } else if (ch == "0" && stream.eat(/x/i)) {
-      stream.eatWhile(/[\da-f]/i);
-      return ret("number", "number");
-    } else if (ch == "0" && stream.eat(/o/i)) {
-      stream.eatWhile(/[0-7]/i);
-      return ret("number", "number");
-    } else if (ch == "0" && stream.eat(/b/i)) {
-      stream.eatWhile(/[01]/i);
+    } else if (ch == "0" && stream.match(/^(?:x[\da-f]+|o[0-7]+|b[01]+)n?/i)) {
       return ret("number", "number");
     } else if (/\d/.test(ch)) {
-      stream.match(/^\d*(?:\.\d*)?(?:[eE][+\-]?\d+)?/);
+      stream.match(/^\d*(?:n|(?:\.\d*)?(?:[eE][+\-]?\d+)?)?/);
       return ret("number", "number");
     } else if (ch == "/") {
       if (stream.eat("*")) {