node.js

/**
 * Module dependencies.
 */

var tty = require('tty');
var util = require('util');

/**
 * This is the Node.js implementation of `debug()`.
 *
 * Expose `debug()` as the module.
 */

exports = module.exports = require('./debug');
exports.init = init;
exports.log = log;
exports.formatArgs = formatArgs;
exports.save = save;
exports.load = load;
exports.useColors = useColors;

/**
 * Colors.
 */

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

/**
 * Build up the default `inspectOpts` object from the environment variables.
 *
 *   $ DEBUG_COLORS=no DEBUG_DEPTH=10 DEBUG_SHOW_HIDDEN=enabled node script.js
 */

exports.inspectOpts = Object.keys(process.env).filter(function (key) {
  return /^debug_/i.test(key);
}).reduce(function (obj, key) {
  // camel-case
  var prop = key
    .substring(6)
    .toLowerCase()
    .replace(/_([a-z])/g, function (_, k) { return k.toUpperCase() });

  // coerce string value into JS value
  var val = process.env[key];
  if (/^(yes|on|true|enabled)$/i.test(val)) val = true;
  else if (/^(no|off|false|disabled)$/i.test(val)) val = false;
  else if (val === 'null') val = null;
  else val = Number(val);

  obj[prop] = val;
  return obj;
}, {});

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

function useColors() {
  return 'colors' in exports.inspectOpts
    ? Boolean(exports.inspectOpts.colors)
    : tty.isatty(process.stderr.fd);
}

/**
 * Map %o to `util.inspect()`, all on a single line.
 */

exports.formatters.o = function(v) {
  this.inspectOpts.colors = this.useColors;
  return util.inspect(v, this.inspectOpts)
    .replace(/\s*\n\s*/g, ' ');
};

/**
 * Map %o to `util.inspect()`, allowing multiple lines if needed.
 */

exports.formatters.O = function(v) {
  this.inspectOpts.colors = this.useColors;
  return util.inspect(v, this.inspectOpts);
};

/**
 * Adds ANSI color escape codes if enabled.
 *
 * @api public
 */

function formatArgs(args) {
  var name = this.namespace;
  var useColors = this.useColors;

  if (useColors) {
    var c = this.color;
    var prefix = '  \u001b[3' + c + ';1m' + name + ' ' + '\u001b[0m';

    args[0] = prefix + args[0].split('\n').join('\n' + prefix);
    args.push('\u001b[3' + c + 'm+' + exports.humanize(this.diff) + '\u001b[0m');
  } else {
    args[0] = new Date().toUTCString()
      + ' ' + name + ' ' + args[0];
  }
}

/**
 * Invokes `util.format()` with the specified arguments and writes to stderr.
 */

function log() {
  return process.stderr.write(util.format.apply(util, arguments) + '\n');
}

/**
 * Save `namespaces`.
 *
 * @param {String} namespaces
 * @api private
 */

function save(namespaces) {
  if (null == namespaces) {
    // If you set a process.env field to null or undefined, it gets cast to the
    // string 'null' or 'undefined'. Just delete instead.
    delete process.env.DEBUG;
  } else {
    process.env.DEBUG = namespaces;
  }
}

/**
 * Load `namespaces`.
 *
 * @return {String} returns the previously persisted debug modes
 * @api private
 */

function load() {
  return process.env.DEBUG;
}

/**
 * Init logic for `debug` instances.
 *
 * Create a new `inspectOpts` object in case `useColors` is set
 * differently for a particular `debug` instance.
 */

function init (debug) {
  debug.inspectOpts = {};

  var keys = Object.keys(exports.inspectOpts);
  for (var i = 0; i < keys.length; i++) {
    debug.inspectOpts[keys[i]] = exports.inspectOpts[keys[i]];
  }
}

/**
 * Enable namespaces listed in `process.env.DEBUG` initially.
 */

exports.enable(load());