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Add color to your JavaScript!


Red Eyed Tree Frog (Agalychnis callidryas)


Takes JavaScript code, along with a config and returns the original code with tokens wrapped and/or replaced as configured.


  • server side using nodejs
  • in the browser

What for?

One usecase is adding metadata to your code that can then be used to apply syntax highlighting.


  • copy the config.js and edit it in order to specify how certain tokens are to be surrounded/replaced
  • replace the undefined of each token you want to configure with one of the following

{String} config


wraps the token inside before/after

{Object} config

{ _before: 'before', _after: 'after' }

wraps token inside before/after

Missing before and after resolution for {String} and {Object} config

For the {String} and {Object} configurations, 'before' or 'after' may be omitted:

  • {String}:
    • 'before:' (omitting 'after')
    • ':after' (omitting 'before')
  • {Object}:
    • { _before: 'before' } (omitting '_after')
    • { _after: 'after' } (omitting '_before')

In these cases the missing half is resolved as follows:

  • from the parent._default (i.e., Keyword._default) if found
  • otherwise from the config._default if found
  • otherwise '' (empty string)

{Function} config

function (tokenString, info) { return {String}|{Object}; }


  • tokenString: the content of the token that is currently being processed
  • info: an object with the following structure
    // {Int}
    // the index of the token being processed inside tokens

    // {Array}
    // all tokens that are being processed including comments 
    // (i.e. the result of merging esprima tokens and comments)
  , tokens
// {Object} // the abstract syntax tree of the parsed code , ast
// {String} // the code that was parsed (same string as the one passed to redeyed(code ..) , code }

In most cases the tokenString is all you need. The extra info object is passed in case you need to gather more information about the token's surroundings in order to decide how to transform it. See: replace-log-example


You can return a {String} or an {Object} from a {Function} config.

  • when returning a {String}, the token value will be replaced with it
  • when returning an {Object}, it should be of the following form:
    // {String}
    // the string that should be substituted for the value of the current and all skipped tokens

    // {Object} (Token)
    // the token after which processing should continue
    // all tokens in between the current one and this one inclusive will be ignored
  , skipPastToken

Transforming JavaScript code

redeyed(code, config[, opts])

Invoke redeyed with your configuration, a code snippet and maybe opts as in the below example:

var redeyed = require('redeyed')
  , config = require('./path/to/config')
  , code = 'var a = 3;'
  , result;

// redeyed will throw an error (caused by the esprima parser) if the code has invalid javascript
try {
  result = redeyed(code, config);
} catch(err) {


{ // {Boolean}
  // if true result.code is not assigned and therefore undefined
  // if false (default) result.code property contains the result of split.join
  nojoin: true|false

return value:

{   ast
, tokens
, comments , splits
, code
  • ast {Array}: abstract syntax tree as returned by esprima parse
  • tokens {Array}: tokens) provided by esprima (excluding comments)
  • comments {Array}: block and line comments as provided by esprima
  • splits {Array}: code pieces split up, some of which where transformed as configured
  • code {String}: transformed code, same as splits.join('') unless this step has been skipped (see opts)

Browser Support


Ensure to include esprima as one of your dependencies

define(['redeyed'], function (redeyed) {
 [ .. ]

Attached to global window object

The redeyed {Function} will be exposed globally as window.redeyed - big surprise!

<script type="text/javascript" src=""></script>
<script type="text/javascript" src="path/to/redeyed.js"></script>

redeyed in the wild

  • cardinal: Syntax highlights JavaScript code with ANSI colors to be printed to the terminal
  • peacock: JavaScript syntax highlighter that generates html that is compatible with pygments styles.