v8/test/mjsunit/es6/microtask-delivery.js

// Copyright 2012 the V8 project authors. All rights reserved.
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// modification, are permitted provided that the following conditions are
// met:
//
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// Flags: --allow-natives-syntax

var ordering = [];
function reset() {
  ordering = [];
}

function assertArrayValues(expected, actual) {
  assertEquals(expected.length, actual.length);
  for (var i = 0; i < expected.length; i++) {
    assertEquals(expected[i], actual[i]);
  }
}

function assertOrdering(expected) {
  %RunMicrotasks();
  assertArrayValues(expected, ordering);
}

function newPromise(id, fn) {
  var r;
  var t = 1;
  var promise = new Promise(function(resolve) {
    r = resolve;
    if (fn) fn();
  });

  var next = promise.then(function(value) {
    ordering.push('p' + id);
    return value;
  });

  return {
    resolve: r,
    then: function(fn) {
      next = next.then(function(value) {
        ordering.push('p' + id + ':' + t++);
        return fn ? fn(value) : value;
      });

      return this;
    }
  };
}

(function PromiseThens() {
  reset();

  var p1 = newPromise(1).then();
  var p2 = newPromise(2).then();

  p1.resolve();
  p2.resolve();

  assertOrdering(['p1', 'p2', 'p1:1', 'p2:1']);
})();