Javascript (node.js) Promise async/await issue

Question

new Promise(async (resolve, reject) =>
{
  try
  {
    await new Promise((resolveSec, rejectSec) =>
    {
      setTimeout(function()
      {
        resolveSec('')
      }, 1000);
    }).then(function(val)
    {
      return reject('should reject') //does not stop execution
      //throw('should reject'); //stops execution
    });
    console.log('not here'); //should not get to here
  }
  catch (err)
  {
    console.log('caught error');
  }
}).catch(function(err)
{
  console.log(err);
});

Could someone explain why the above code does not end execution on "reject" but it works with "throw" as I thought that both "reject" and "throw" inside Promise have same functionality.

Probably has to do with this: https://stackoverflow.com/questions/33445415/javascript-promises-reject-vs-throw — Daniel Gale, Apr 19 '18 at 14:07
That's not how Promises are meant to be used. The *entire idea* of Promises is to uncouple sequential asynchronous operations, and here you've got them nested...that's an anti-pattern. — Jared Smith, Apr 19 '18 at 14:07
Calling reject would reject the outer promises, not the one inside the `try` block. — Felix Kling, Apr 19 '18 at 14:08
Also note that in practice you should almost never use `new Promise` — Benjamin Gruenbaum, Apr 19 '18 at 14:10
@BenjaminGruenbaum especially if you are using async/await which does the Promise wrapping for you. — zero298, Apr 19 '18 at 14:11
@BenjaminGruenbaum why not use `new Promise`? `Promise.resolve` is just a syntactic sugar. — dfilkovi, Apr 19 '18 at 14:19

score 0 · Accepted Answer · answered Apr 19 '18 at 14:10

Cause throw ends the inner Promises execution, which will then be rethrown by the await statement, ending the execution of the outer Promise. reject however will set the outer promises state to rejected, return will end the execution of the inner promisee function but not of the outer one.

Javascript (node.js) Promise async/await issue

1 Answers1