Check out example codes for "typescript promise". It will help you in understanding the concepts better.

Code Example 1

new Promise<boolean>((res, rej) => {
  res(true);
})
.then(res => {
  console.log(res);
  return false;
})
  .then(res => {
  console.log(res);
  return true;
})
  .then(res => {
  console.log(res);
})
  .catch(error => {
  console.log('ERROR:', error.message);
});

Learn ReactJs, React Native from akashmittal.com