browser.js

/**
 * This is the web browser implementation of `debug()`.
 *
 * Expose `debug()` as the module.
 */

exports = module.exports = require('./debug');
exports.log = log;
exports.formatArgs = formatArgs;
exports.save = save;
exports.load = load;
exports.useColors = useColors;
exports.storage = 'undefined' != typeof chrome
               && 'undefined' != typeof chrome.storage
                  ? chrome.storage.local
                  : localstorage();

/**
 * Colors.
 */

exports.colors = [
  'lightseagreen',
  'forestgreen',
  'goldenrod',
  'dodgerblue',
  'darkorchid',
  'crimson'
];

/**
 * Currently only WebKit-based Web Inspectors, Firefox >= v31,
 * and the Firebug extension (any Firefox version) are known
 * to support "%c" CSS customizations.
 *
 * TODO: add a `localStorage` variable to explicitly enable/disable colors
 */

function useColors() {
  // is webkit? http://stackoverflow.com/a/16459606/376773
  // document is undefined in react-native: https://github.com/facebook/react-native/pull/1632
  return (typeof document !== 'undefined' && 'WebkitAppearance' in document.documentElement.style) ||
    // is firebug? http://stackoverflow.com/a/398120/376773
    (window.console && (console.firebug || (console.exception && console.table))) ||
    // is firefox >= v31?
    // https://developer.mozilla.org/en-US/docs/Tools/Web_Console#Styling_messages
    (navigator.userAgent.toLowerCase().match(/firefox\/(\d+)/) && parseInt(RegExp.$1, 10) >= 31);
}

/**
 * Map %j to `JSON.stringify()`, since no Web Inspectors do that by default.
 */

exports.formatters.j = function(v) {
  return JSON.stringify(v);
};


/**
 * Colorize log arguments if enabled.
 *
 * @api public
 */

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

  args[0] = (useColors ? '%c' : '')
    + this.namespace
    + (useColors ? ' %c' : ' ')
    + args[0]
    + (useColors ? '%c ' : ' ')
    + '+' + exports.humanize(this.diff);

  if (!useColors) return args;

  var c = 'color: ' + this.color;
  args = [args[0], c, 'color: inherit'].concat(Array.prototype.slice.call(args, 1));

  // the final "%c" is somewhat tricky, because there could be other
  // arguments passed either before or after the %c, so we need to
  // figure out the correct index to insert the CSS into
  var index = 0;
  var lastC = 0;
  args[0].replace(/%[a-z%]/g, function(match) {
    if ('%%' === match) return;
    index++;
    if ('%c' === match) {
      // we only are interested in the *last* %c
      // (the user may have provided their own)
      lastC = index;
    }
  });

  args.splice(lastC, 0, c);
  return args;
}

/**
 * Invokes `console.log()` when available.
 * No-op when `console.log` is not a "function".
 *
 * @api public
 */

function log() {
  // this hackery is required for IE8/9, where
  // the `console.log` function doesn't have 'apply'
  return 'object' === typeof console
    && console.log
    && Function.prototype.apply.call(console.log, console, arguments);
}

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

function save(namespaces) {
  try {
    if (null == namespaces) {
      exports.storage.removeItem('debug');
    } else {
      exports.storage.debug = namespaces;
    }
  } catch(e) {}
}

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

function load() {
  var r;
  try {
    r = exports.storage.debug;
  } catch(e) {}
  return r;
}

/**
 * Enable namespaces listed in `localStorage.debug` initially.
 */

exports.enable(load());

/**
 * Localstorage attempts to return the localstorage.
 *
 * This is necessary because safari throws
 * when a user disables cookies/localstorage
 * and you attempt to access it.
 *
 * @return {LocalStorage}
 * @api private
 */

function localstorage(){
  try {
    return window.localStorage;
  } catch (e) {}
}