react/packages/shared/ReactErrorUtils.js

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

import invariant from 'fbjs/lib/invariant';

const ReactErrorUtils = {
  // Used by Fiber to simulate a try-catch.
  _caughtError: (null: mixed),
  _hasCaughtError: (false: boolean),

  // Used by event system to capture/rethrow the first error.
  _rethrowError: (null: mixed),
  _hasRethrowError: (false: boolean),

  injection: {
    injectErrorUtils(injectedErrorUtils: Object) {
      invariant(
        typeof injectedErrorUtils.invokeGuardedCallback === 'function',
        'Injected invokeGuardedCallback() must be a function.',
      );
      invokeGuardedCallback = injectedErrorUtils.invokeGuardedCallback;
    },
  },

  /**
   * Call a function while guarding against errors that happens within it.
   * Returns an error if it throws, otherwise null.
   *
   * In production, this is implemented using a try-catch. The reason we don't
   * use a try-catch directly is so that we can swap out a different
   * implementation in DEV mode.
   *
   * @param {String} name of the guard to use for logging or debugging
   * @param {Function} func The function to invoke
   * @param {*} context The context to use when calling the function
   * @param {...*} args Arguments for function
   */
  invokeGuardedCallback: function<A, B, C, D, E, F, Context>(
    name: string | null,
    func: (a: A, b: B, c: C, d: D, e: E, f: F) => void,
    context: Context,
    a: A,
    b: B,
    c: C,
    d: D,
    e: E,
    f: F,
  ): void {
    invokeGuardedCallback.apply(ReactErrorUtils, arguments);
  },

  /**
   * Same as invokeGuardedCallback, but instead of returning an error, it stores
   * it in a global so it can be rethrown by `rethrowCaughtError` later.
   * TODO: See if _caughtError and _rethrowError can be unified.
   *
   * @param {String} name of the guard to use for logging or debugging
   * @param {Function} func The function to invoke
   * @param {*} context The context to use when calling the function
   * @param {...*} args Arguments for function
   */
  invokeGuardedCallbackAndCatchFirstError: function<A, B, C, D, E, F, Context>(
    name: string | null,
    func: (a: A, b: B, c: C, d: D, e: E, f: F) => void,
    context: Context,
    a: A,
    b: B,
    c: C,
    d: D,
    e: E,
    f: F,
  ): void {
    ReactErrorUtils.invokeGuardedCallback.apply(this, arguments);
    if (ReactErrorUtils.hasCaughtError()) {
      const error = ReactErrorUtils.clearCaughtError();
      if (!ReactErrorUtils._hasRethrowError) {
        ReactErrorUtils._hasRethrowError = true;
        ReactErrorUtils._rethrowError = error;
      }
    }
  },

  /**
   * During execution of guarded functions we will capture the first error which
   * we will rethrow to be handled by the top level error handler.
   */
  rethrowCaughtError: function() {
    return rethrowCaughtError.apply(ReactErrorUtils, arguments);
  },

  hasCaughtError: function() {
    return ReactErrorUtils._hasCaughtError;
  },

  clearCaughtError: function() {
    if (ReactErrorUtils._hasCaughtError) {
      const error = ReactErrorUtils._caughtError;
      ReactErrorUtils._caughtError = null;
      ReactErrorUtils._hasCaughtError = false;
      return error;
    } else {
      invariant(
        false,
        'clearCaughtError was called but no error was captured. This error ' +
          'is likely caused by a bug in React. Please file an issue.',
      );
    }
  },
};

let invokeGuardedCallback = function(name, func, context, a, b, c, d, e, f) {
  ReactErrorUtils._hasCaughtError = false;
  ReactErrorUtils._caughtError = null;
  const funcArgs = Array.prototype.slice.call(arguments, 3);
  try {
    func.apply(context, funcArgs);
  } catch (error) {
    ReactErrorUtils._caughtError = error;
    ReactErrorUtils._hasCaughtError = true;
  }
};

if (__DEV__) {
  // In DEV mode, we swap out invokeGuardedCallback for a special version
  // that plays more nicely with the browser's DevTools. The idea is to preserve
  // "Pause on exceptions" behavior. Because React wraps all user-provided
  // functions in invokeGuardedCallback, and the production version of
  // invokeGuardedCallback uses a try-catch, all user exceptions are treated
  // like caught exceptions, and the DevTools won't pause unless the developer
  // takes the extra step of enabling pause on caught exceptions. This is
  // untintuitive, though, because even though React has caught the error, from
  // the developer's perspective, the error is uncaught.
  //
  // To preserve the expected "Pause on exceptions" behavior, we don't use a
  // try-catch in DEV. Instead, we synchronously dispatch a fake event to a fake
  // DOM node, and call the user-provided callback from inside an event handler
  // for that fake event. If the callback throws, the error is "captured" using
  // a global event handler. But because the error happens in a different
  // event loop context, it does not interrupt the normal program flow.
  // Effectively, this gives us try-catch behavior without actually using
  // try-catch. Neat!

  // Check that the browser supports the APIs we need to implement our special
  // DEV version of invokeGuardedCallback
  if (
    typeof window !== 'undefined' &&
    typeof window.dispatchEvent === 'function' &&
    typeof document !== 'undefined' &&
    typeof document.createEvent === 'function'
  ) {
    const fakeNode = document.createElement('react');

    const invokeGuardedCallbackDev = function(
      name,
      func,
      context,
      a,
      b,
      c,
      d,
      e,
      f,
    ) {
      // Keeps track of whether the user-provided callback threw an error. We
      // set this to true at the beginning, then set it to false right after
      // calling the function. If the function errors, `didError` will never be
      // set to false. This strategy works even if the browser is flaky and
      // fails to call our global error handler, because it doesn't rely on
      // the error event at all.
      let didError = true;

      // Create an event handler for our fake event. We will synchronously
      // dispatch our fake event using `dispatchEvent`. Inside the handler, we
      // call the user-provided callback.
      const funcArgs = Array.prototype.slice.call(arguments, 3);
      function callCallback() {
        // We immediately remove the callback from event listeners so that
        // nested `invokeGuardedCallback` calls do not clash. Otherwise, a
        // nested call would trigger the fake event handlers of any call higher
        // in the stack.
        fakeNode.removeEventListener(evtType, callCallback, false);
        func.apply(context, funcArgs);
        didError = false;
      }

      // Create a global error event handler. We use this to capture the value
      // that was thrown. It's possible that this error handler will fire more
      // than once; for example, if non-React code also calls `dispatchEvent`
      // and a handler for that event throws. We should be resilient to most of
      // those cases. Even if our error event handler fires more than once, the
      // last error event is always used. If the callback actually does error,
      // we know that the last error event is the correct one, because it's not
      // possible for anything else to have happened in between our callback
      // erroring and the code that follows the `dispatchEvent` call below. If
      // the callback doesn't error, but the error event was fired, we know to
      // ignore it because `didError` will be false, as described above.
      let error;
      // Use this to track whether the error event is ever called.
      let didSetError = false;
      let isCrossOriginError = false;

      function onError(event) {
        error = event.error;
        didSetError = true;
        if (error === null && event.colno === 0 && event.lineno === 0) {
          isCrossOriginError = true;
        }
      }

      // Create a fake event type.
      const evtType = `react-${name ? name : 'invokeguardedcallback'}`;

      // Attach our event handlers
      window.addEventListener('error', onError);
      fakeNode.addEventListener(evtType, callCallback, false);

      // Synchronously dispatch our fake event. If the user-provided function
      // errors, it will trigger our global error handler.
      const evt = document.createEvent('Event');
      evt.initEvent(evtType, false, false);
      fakeNode.dispatchEvent(evt);

      if (didError) {
        if (!didSetError) {
          // The callback errored, but the error event never fired.
          error = new Error(
            'An error was thrown inside one of your components, but React ' +
              "doesn't know what it was. This is likely due to browser " +
              'flakiness. React does its best to preserve the "Pause on ' +
              'exceptions" behavior of the DevTools, which requires some ' +
              "DEV-mode only tricks. It's possible that these don't work in " +
              'your browser. Try triggering the error in production mode, ' +
              'or switching to a modern browser. If you suspect that this is ' +
              'actually an issue with React, please file an issue.',
          );
        } else if (isCrossOriginError) {
          error = new Error(
            "A cross-origin error was thrown. React doesn't have access to " +
              'the actual error object in development. ' +
              'See https://fb.me/react-crossorigin-error for more information.',
          );
        }
        ReactErrorUtils._hasCaughtError = true;
        ReactErrorUtils._caughtError = error;
      } else {
        ReactErrorUtils._hasCaughtError = false;
        ReactErrorUtils._caughtError = null;
      }

      // Remove our event listeners
      window.removeEventListener('error', onError);
    };

    invokeGuardedCallback = invokeGuardedCallbackDev;
  }
}

let rethrowCaughtError = function() {
  if (ReactErrorUtils._hasRethrowError) {
    const error = ReactErrorUtils._rethrowError;
    ReactErrorUtils._rethrowError = null;
    ReactErrorUtils._hasRethrowError = false;
    throw error;
  }
};

export default ReactErrorUtils;