extensions/renderer/resources/uncaught_exception_handler.js

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Handles uncaught exceptions thrown by extensions. By default this is to
// log an error message, but tests may override this behaviour.
var handler = function(message, e) {
  console.error(message);
};

/**
 * Formats the error message and invokes the error handler.
 *
 * @param {string} message - Error message prefix.
 * @param {Error|*} e - Thrown object.
 * @param {string=} priorStackTrace - Error message suffix.
 * @see formatErrorMessage
 */
function handle(message, e, priorStackTrace) {
  message = formatErrorMessage(message, e, priorStackTrace);
  handler(message, e);
}

// Runs a user-supplied callback safely.
function safeCallbackApply(name, request, callback, args) {
  try {
    $Function.apply(callback, request, args);
  } catch (e) {
    handle('Error in response to ' + name, e, request.stack);
  }
}

/**
 * Append the error description and stack trace to |message|.
 *
 * @param {string} message - The prefix of the error message.
 * @param {Error|*} e - The thrown error object. This object is potentially
 *   unsafe, because it could be generated by an extension.
 * @param {string=} priorStackTrace - The stack trace to be appended to the
 *   error message. This stack trace must not include stack frames of |e.stack|,
 *   because both stack traces are concatenated. Overlapping stack traces will
 *   confuse extension developers.
 * @return {string} The formatted error message.
 */
function formatErrorMessage(message, e, priorStackTrace) {
  if (e)
    message += ': ' + safeErrorToString(e, false);

  var stack;
  try {
    // If the stack was set, use it.
    // |e.stack| could be void in the following common example:
    // throw "Error message";
    stack = $String.self(e && e.stack);
  } catch (e) {}

  // If a stack is not provided, capture a stack trace.
  if (!priorStackTrace && !stack)
    stack = getStackTrace();

  stack = filterExtensionStackTrace(stack);
  if (stack)
    message += '\n' + stack;

  // If an asynchronouse stack trace was set, append it.
  if (priorStackTrace)
    message += '\n' + priorStackTrace;

  return message;
}

function filterExtensionStackTrace(stack) {
  if (!stack)
    return '';
  // Remove stack frames in the stack trace that weren't associated with the
  // extension, to not confuse extension developers with internal details.
  stack = $String.split(stack, '\n');
  stack = $Array.filter(stack, function(line) {
    return $String.indexOf(line, 'chrome-extension://') >= 0;
  });
  return $Array.join(stack, '\n');
}

function getStackTrace() {
  var e = {};
  $Error.captureStackTrace(e, getStackTrace);
  return e.stack;
}

function getExtensionStackTrace() {
  return filterExtensionStackTrace(getStackTrace());
}

/**
 * Convert an object to a string.
 *
 * @param {Error|*} e - A thrown object (possibly user-supplied).
 * @param {boolean=} omitType - Whether to try to serialize |e.message| instead
 *   of |e.toString()|.
 * @return {string} The error message.
 */
function safeErrorToString(e, omitType) {
  try {
    return $String.self(omitType && e.message || e);
  } catch (e) {
    // This error is exceptional and could be triggered by
    // throw {toString: function() { throw 'Haha' } };
    return '(cannot get error message)';
  }
}

exports.$set('handle', handle);

// |newHandler| A function which matches |handler|.
exports.$set('setHandler', function(newHandler) {
  handler = newHandler;
});

exports.$set('safeCallbackApply', safeCallbackApply);
exports.$set('getStackTrace', getStackTrace);
exports.$set('getExtensionStackTrace', getExtensionStackTrace);
exports.$set('safeErrorToString', safeErrorToString);