src/js/promise.js

// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

(function(global, utils, extrasUtils) {

"use strict";

%CheckIsBootstrapping();

// -------------------------------------------------------------------
// Imports

var InternalArray = utils.InternalArray;
var promiseHandledBySymbol =
    utils.ImportNow("promise_handled_by_symbol");
var promiseForwardingHandlerSymbol =
    utils.ImportNow("promise_forwarding_handler_symbol");
var GlobalPromise = global.Promise;

// -------------------------------------------------------------------
// Define exported functions.

// Combinators.

// ES#sec-promise.all
// Promise.all ( iterable )
function PromiseAll(iterable) {
  if (!IS_RECEIVER(this)) {
    throw %make_type_error(kCalledOnNonObject, "Promise.all");
  }

  // false debugEvent so that forwarding the rejection through all does not
  // trigger redundant ExceptionEvents
  var deferred = %new_promise_capability(this, false);
  var resolutions = new InternalArray();
  var count;

  // For catch prediction, don't treat the .then calls as handling it;
  // instead, recurse outwards.
  var instrumenting = DEBUG_IS_ACTIVE;
  if (instrumenting) {
    SET_PRIVATE(deferred.reject, promiseForwardingHandlerSymbol, true);
  }

  function CreateResolveElementFunction(index, values, promiseCapability) {
    var alreadyCalled = false;
    return (x) => {
      if (alreadyCalled === true) return;
      alreadyCalled = true;
      values[index] = x;
      if (--count === 0) {
        var valuesArray = [];
        %MoveArrayContents(values, valuesArray);
        %_Call(promiseCapability.resolve, UNDEFINED, valuesArray);
      }
    };
  }

  try {
    var i = 0;
    count = 1;
    for (var value of iterable) {
      var nextPromise = this.resolve(value);
      ++count;
      var throwawayPromise = nextPromise.then(
          CreateResolveElementFunction(i, resolutions, deferred),
          deferred.reject);
      // For catch prediction, mark that rejections here are semantically
      // handled by the combined Promise.
      if (instrumenting && %is_promise(throwawayPromise)) {
        SET_PRIVATE(throwawayPromise, promiseHandledBySymbol, deferred.promise);
      }
      ++i;
    }

    // 6.d
    if (--count === 0) {
      var valuesArray = [];
      %MoveArrayContents(resolutions, valuesArray);
      %_Call(deferred.resolve, UNDEFINED, valuesArray);
    }

  } catch (e) {
    %_Call(deferred.reject, UNDEFINED, e);
  }
  return deferred.promise;
}

// ES#sec-promise.race
// Promise.race ( iterable )
function PromiseRace(iterable) {
  if (!IS_RECEIVER(this)) {
    throw %make_type_error(kCalledOnNonObject, PromiseRace);
  }

  // false debugEvent so that forwarding the rejection through race does not
  // trigger redundant ExceptionEvents
  var deferred = %new_promise_capability(this, false);

  // For catch prediction, don't treat the .then calls as handling it;
  // instead, recurse outwards.
  var instrumenting = DEBUG_IS_ACTIVE;
  if (instrumenting) {
    SET_PRIVATE(deferred.reject, promiseForwardingHandlerSymbol, true);
  }

  try {
    for (var value of iterable) {
      var throwawayPromise = this.resolve(value).then(deferred.resolve,
                                                      deferred.reject);
      // For catch prediction, mark that rejections here are semantically
      // handled by the combined Promise.
      if (instrumenting && %is_promise(throwawayPromise)) {
        SET_PRIVATE(throwawayPromise, promiseHandledBySymbol, deferred.promise);
      }
    }
  } catch (e) {
    %_Call(deferred.reject, UNDEFINED, e);
  }
  return deferred.promise;
}

// -------------------------------------------------------------------
// Install exported functions.

utils.InstallFunctions(GlobalPromise, DONT_ENUM, [
  "all", PromiseAll,
  "race", PromiseRace,
]);

})