AsyncYield

My implementation of async await using generator functions

installation

npm install --save async-yield

usage

var async = require('async-yield');

// test
function waitAndResolve(res) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(res);
    }, 10);
  });
}

function waitAndReject(err) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      reject(err);
    }, 10);
  });
}

function throwImmediateError(err) {
  throw err;
}

var runResolves = async(function*(res1, res2) {
  var results = [];

  // resolving promise
  results.push(yield waitAndResolve(res1));

  // no promise - just a plain js value
  results.push(yield res2);

  // this value will resolve the final async promise
  return results;
});

var runErrors = async(function*(err1, err2) {
  var errors = [];

  // rejecting promise
  try {
    yield waitAndReject(err1);
  } catch(e) {
    errors.push(e);
  }

  // no promise - just a simple exception thrown
  try {
    yield throwImmediateError(err2);
  } catch(e) {
    errors.push(e);
  }

  // this will reject the final async promise
  throw errors;
});

runResolves('result 1', 'result 2').then(console.log);
// [ 'result 1', 'result 2' ]

runErrors('error 1', 'error 2').catch(console.error);
// [ 'error 1', 'error 2' ]

testing async functions

When you test your async functions, you might want to inspect the intermediate resolved and rejected yield values. You can do this by calling the yieldAll method.

An example using mocha

var assert = require('assert');

var runErrorsYA = async(function*(err1, err2, err3) {
  try {
    yield waitAndReject(err1);
  } catch(e) {
    console.error(e);
  }

  try {
    yield throwImmediateError(err2);
  } catch(e) {
    console.error(e);
  }

  throw err3;
});

var runResolvesYA = async(function*(res1, res2, res3) {
  yield waitAndResolve(res1);

  yield res2;

  return res3;
});

it('test yieldAll for errors', done => {
  runErrorsYA.yieldAll('error 1', 'error 2', 'error 3')
  .then(res => done(new Error("shouldn't resolve: " + res)))
  .catch(errors => {
    // only rejected promises and uncaught errors should be listed, that's why 'error 2' is not
    // expected to show up
    assert.deepEqual(errors, ['error 1', 'error 3']);
    done();
  })
  .catch(err => done(err));
});

it('test yieldAll value resolving', done => {
  runResolvesYA.yieldAll('hello 1', 'hello 2', 'no promise')
  .then(results => {
    assert.deepEqual(results, ['hello 1', 'hello 2', 'no promise']);
    done();
  })
  .catch(err => done(err));
});

build and test

npm install

npm test

or

node runTests