rbren

let p = Promise.resolve();
p.then(_ => {throw new Error("whoops!")})
p.then(_ => {
  console.log('hello!'); // 'hello!'
})

let q = Promise.resolve();
q = q.then(_ => {throw new Error("whoops!")})
q = q.then(_ => {
  console.log('hello'); // We never reach here

rbren

let p = Promise.resolve('a');
p.then(_ => 'b');
p.then(result => {
  console.log(result) // 'a'
})

let q = Promise.resolve('a');
q = q.then(_ => 'b');
q = q.then(result => {
  console.log(result) // 'b'

rbren

function readFileAndMaybeLock(filename, createLockFile) {
  let promise = Promise.resolve();

  if (createLockFile) {
    promise.then(_ => writeFilePromise(filename + '.lock', ''))
  }

  return promise.then(_ => readFilePromise(filename));
}

rbren

function readFileAndMaybeLock(filename, createLockFile) {
  let promise = Promise.resolve();

  if (createLockFile) {
    promise = promise.then(_ => writeFilePromise(filename + '.lock', ''))
  }

  return promise.then(_ => readFilePromise(filename));
}

rbren

api.getItem(1)
  .then(item => {
    item.amount++;
    api.updateItem(1, item);
  })
  .then(update => {
    return api.deleteItem(1);
  })
  .then(deletion => {
    console.log('done!');

rbren

api.getItem(1)
  .then(item => {
    item.amount++;
    return api.updateItem(1, item);
  })
  .then(update => {
    return api.deleteItem(1);
  })
  .then(deletion => {
    console.log('done!');

rbren

api.getItem(1)
  .then(item => {
    item.amount++;
    api.updateItem(1, item)
      .then(update => {
        api.deleteItem(1)
          .then(deletion => {
            console.log('done!');
          })
      })

rbren

Promise.resolve()
  .then(_ => api.getItem(1))
  .catch(e => api.createItem(1, {amount: 0}))
  .then(item => {
    item.amount++;
    return api.updateItem(1, item);
  })
  .catch(e => {
    console.log('failed to update item');
  })

rbren

Promise.resolve()
  .then(_ => api.getItem(1))
  .then(item => {
    item.amount++;
    return api.updateItem(1, item);
  })
  .catch(e => {
    console.log('failed to get or update item');
  })

rbren

function timeout(ms) {
  return new Promise((resolve, reject) => {
    setTimeout(reject, ms);
  })
}

Promise.race([readFilePromise('index.html'), timeout(1000)])
  .then(data => console.log(data))
  .catch(e => console.log("Timed out after 1 second"))