index.js

var slash, cwd, Mocha, Runner, env, is;

/*
 * load things differently if you're in node.js or the browser.
 */

if (typeof document === 'undefined') {
  is     = { node: true };
  slash  = require('path').sep || '/';
  cwd    = process.cwd() + slash;
  Mocha  = require('mocha');
  Runner = Mocha.Runner;
  env    = function () { return process.env; };
} else {
  is     = { browser: true };
  slash  = '/';
  cwd    = location.href.replace(/\/[^\/]*$/, '/');
  Mocha  = this.Mocha;
  Runner = Mocha.Runner;
  env    = function () { return {}; };
}

/*
 * for the browser: allow the user to specify things to be ignored
 */

if (is.browser && mocha && !mocha.traceIgnores)
  mocha.traceIgnores = ['mocha.js'];

/*
 * monkey-patch Runner#fail to modify `err`.
 */

var old = Runner.prototype.fail;
Runner.prototype.fail = function (test, err) {
  err = __mocha_internal__cleanError(err);
  return old.call(this, test, err);
};

/*
 * cleans an error.
 */

function __mocha_internal__cleanError (e) {
  if (!e.stack) return e;
  var stack = e.stack.split('\n');

  stack = stack.reduce(function (list, line) {
    // Strip out certain lines.
    if (is.node && (isNodeModule(line) ||
      isMochaInternal(line) ||
      isNodeInternal(line) ||
      isMochaCleanInternal(line)))
      return list;

    if (is.browser && (
      isBrowserIgnored(line) ||
      isMochaCleanInternal(line)))
      return list;

    // Clean up cwd.
    if (!env().SHOW_ABSOLUTE_PATHS)
      line = line.replace(cwd, '');

    // experimental: show errors in a format
    // like "example/foo.js:10:19: at functionName"
    if (env().FILENAMES_FIRST)
      line = reorderFilename(line);

    list.push(line);
    return list;
  }, []);

  e.stack = stack.join('\n');
  return e;
}

/*
 * detect if a line is from a 3rd-party module.
 */

function isNodeModule (line) {
  return (~line.indexOf('node_modules')) &&
    !env().SHOW_NODE_MODULES;
}

/*
 * detect stuff from mocha itself.
 * usually not needed, but if SHOW_NODE_MODULES is on, you probably wanna
 * supress this.
 */

function isMochaInternal (line) {
  return (~line.indexOf('node_modules' + slash + 'mocha'));
}

/*
 * detect stuff ignored in the browser.
 */

function isBrowserIgnored (line) {
  var ignores = mocha.traceIgnores || [];

  for (var i = 0, len = ignores.length; i < len; i++) {
    var spec = ignores[i];

    if ((typeof spec === 'string' && ~line.indexOf(spec)) ||
      (typeof spec === 'function' && spec(line)) ||
      (spec instanceof RegExp && line.match(spec)))
      return true;
  }
}

/*
 * detect stuff from this library.
 */

function isMochaCleanInternal (line) {
  return (~line.indexOf('__mocha_internal__'));
}

/*
 * detect internal node errors. Examples:
 *
 *   at Module._compile (module.js:439:25)
 *   at Object.Module._extensions..js (module.js:474:10)
 *   at Module.load (module.js:356:32)
 *   at Function.Module._load (module.js:312:12)
 *   at Module.require (module.js:364:17)
 *   at require (module.js:380:17)
 *   at process._tickCallback (node.js:415:13)
 */

function isNodeInternal (line) {
  return false ||
    (~line.indexOf('(timers.js:')) ||
    (~line.indexOf('(node.js:')) ||
    (~line.indexOf('(module.js:')) ||
    (~line.indexOf('(domain.js:')) ||
    (~line.indexOf('GeneratorFunctionPrototype.next (native)')) ||
    false;
}

/*
 * puts filenames first.
 *
 *     "   at foobar (example.js:2:3)"
 *     => "example.js:2:3: foobar"
 *
 *     "   at example.js:2:3"
 *     => "example.js:2:3:"
 */

function reorderFilename (line) {
  var m;
  m = line.match(/^(\s*)at (.*?) \(native\)$/);
  if (m) return "" + m[1] + "[native]: " + m[2];

  m = line.match(/^(\s*)at (.*?) \((.*?)\)$/);
  if (m) return "" + m[1] + m[3] + ": " + m[2];

  m = line.match(/^(\s*)at (.*?)$/);
  if (m) return "" + m[1] + m[2] + ":";

  return line;
}

/*
 * export for tests.
 */

if (typeof module === 'object') {
  exports.cleanError = __mocha_internal__cleanError;
  exports.reorderFilename = reorderFilename;
}