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regular expression alternation for tokenizers

What is this?

This allows joining regular expressions mainly for the purpose of constructing tokenizers.


This library emulates to some degree the new sticky /y flag. The sticky flag has 3 basic effects on a regular expression.

  1. Implicit /g
  2. Not looking past lastIndex
  3. Treating the string as if it starts at lastIndex.

The first one if obvious, we simply default to /g. The second one is a little more complex, but we manage. If a match looks forward, the exec() method will reject the match.

Only the last one do we not support. It would require making a partial copy of the string per match which would have a significant overhead with little or no gain. Only when then /y flag is widely adopted will this be possible.

Add Specification

var re = new ReMix();
re.add(/regexp/);       // RegExp 
re.add(function () {    // {@link ReMix~SetupCallback} 
 return {               // {@link ReMix~NamedRegExp} 
   name: "foo"
   spec: [              // {@link ReMix~Spec}[] 
     {                  // {@link ReMix~Pairs} 
       baz: 'foo{eol}$' // {@link ReMix~Template} 
     function () {      // {@link ReMix~SetupCallback} 
       return /bar/


Regular expressions are combined if their flags, which are not in defaultFlags are the same. In other words, defaultFlags are ignored for the purpose of comparing.

/* combines */
var re = new Re([/foo/, /bar/g]); // /g is defualt flag 
console.log(re.compile()); // [/(foo)|(bar)/] 
/* does not combine */
var re = new Re([/foo/, /bar/i]);
console.log(re.compile()); // [/(foo)/, /(bar)/i] 


Each regular expression can be named and have sub-named expressions which are tracked by namespaces with configurable delimiters. ReMix object can also compose other ReMix objects which are also namespaced into the current level.

Namespaces are returned as the second element in the match array returned by exec().

var re = new ReMix('foobar', /foo(bar)/, { bar: /bar/, baz: { boo: /boo/ } });
var str = "foobarboobarfoobar", match;
match = re.exec(str); // [ [ 'foobar', 'bar' ], 'foobar',         0,  6 ] 
match = re.exec(str); // [ [ 'boo'           ], '', 2,  9 ] 
match = re.exec(str); // [ [ 'bar'           ], '',     1, 12 ] 
match = re.exec(str); // [ [ 'foobar', 'bar' ], 'foobar',         0, 18 ] 
match = re.exec(str); // false 
var a1 = new ReMix('a1'),
    a2 = new ReMix('a2'),
   str = "foobar";
a1.options({nsDelimiter: '/'});
a1.add({foo: /foo/});
a2.add({bar: /bar/});
console.log(a1.exec(str)); // [['foo'], 'a1/foo',    0, 3] 
console.log(a1.exec(str)); // [['foo'], 'a1/a2/bar', 1, 6] 


Templates are a very simple way to compose regular expressesion. Templates can be used in the place of regular expressions. You can register new templates or use the existing predefined templates. Here is a list:

  • hspace - Horizontal space, including unicode horizontal space code points

  • noHspace - hspace negated

  • vspace - Vertical space character class

  • number - General number match, includes all Javascript supported number formated

  • noVspace - Negated vspace character class

  • space - /\s/

  • noSpace - /\S/

  • word - /\w/

  • noWord - /\W/

  • any - Match any one character, doesn't depend on RegExp flags

  • eol - Match EOL on any platform

  • notEol- Not EOL character class

  • end - END of string or line depending on RegExp flags

  • begin - Beginning of line or string depending on RegExp flags

Registering a template has two formats:

ReMix.register('eol',        /(?:\r\n?|\n|\f)/);
ReMix.register('emptyLines', '{eol}{eol+}');
  cMultiComment: /\/\*[^*]*\*+(?:[^\/*][^*]*\*+)*\//,
  cLineComment:  "//{notEol*}{eol}"

Example of how templates integrate with ReMix.

ReMix.register('matchFoo', /foo/);
var remix = new ReMix('foo', 'matchFoo');
var remix = new ReMix('bar', '{matchFoo*}|bar');
ReMix.register('matchFooOrBar', '{matchFoo}|bar');
var remix = new ReMix('bax', '\\s*{matchFooOrBar+}\\s*');


Please report bug here.

This is BETA software. Please report bugs or submit PR's.

Although I know of no bugs, the current test coverage is not complete.


  • Complete test coverage.
  • Add browser tests.
  • Add travis.
  • Add badges.
  • Better, less contrived examples.
  • More information in this


ReMix Class API Documentation


Copyright (C) 2014 Scott Beck, all rights reserved

Licensed under the MIT license