debug.js

/**
 * Module dependencies.
 */

var tty = require('tty');

/**
 * Expose `debug()` as the module.
 */

module.exports = debug;

/**
 * Enabled debuggers.
 */

var names = []
  , skips = [];

(process.env.DEBUG || '')
  .split(/[\s,]+/)
  .forEach(function(name){
    name = name.replace('*', '.*?');
    if (name[0] === '-') {
      skips.push(new RegExp('^' + name.substr(1) + '$'));
    } else {
      names.push(new RegExp('^' + name + '$'));
    }
  });

/**
 * Colors.
 */

var colors = [6, 2, 3, 4, 5, 1];

/**
 * Previous debug() call.
 */

var prev = {};

/**
 * Previously assigned color.
 */

var prevColor = 0;

/**
 * Is stdout a TTY? Colored output is disabled when `true`.
 */

var isatty = tty.isatty(2);

/**
 * Select a color.
 *
 * @return {Number}
 * @api private
 */

function color() {
  return colors[prevColor++ % colors.length];
}

/**
 * Humanize the given `ms`.
 *
 * @param {Number} m
 * @return {String}
 * @api private
 */

function humanize(ms) {
  var sec = 1000
    , min = 60 * 1000
    , hour = 60 * min;

  if (ms >= hour) return (ms / hour).toFixed(1) + 'h';
  if (ms >= min) return (ms / min).toFixed(1) + 'm';
  if (ms >= sec) return (ms / sec | 0) + 's';
  return ms + 'ms';
}

/**
 * Create a debugger with the given `name`.
 *
 * @param {String} name
 * @return {Type}
 * @api public
 */

function debug(name) {
  function disabled(){}
  disabled.enabled = false;

  var match = skips.some(function(re){
    return re.test(name);
  });

  if (match) return disabled;

  match = names.some(function(re){
    return re.test(name);
  });

  if (!match) return disabled;
  var c = color();

  function colored(fmt) {
    var curr = new Date;
    var ms = curr - (prev[name] || curr);
    prev[name] = curr;

    fmt = '  \033[9' + c + 'm' + name + ' '
      + '\033[3' + c + 'm\033[90m'
      + fmt + '\033[3' + c + 'm'
      + ' +' + humanize(ms) + '\033[0m';

    console.error.apply(this, arguments);
  }

  function plain(fmt) {
    fmt = new Date().toUTCString()
      + ' ' + name + ' ' + fmt;
    console.error.apply(this, arguments);
  }

  colored.enabled = plain.enabled = true;

  return isatty
    ? colored
    : plain;
}