Bluebird.JS Promise: new Promise(function (resolve, reject){}) vs Promise.try(function(){})

Question

When should I use which? Are the following the same?

new Promise() example:

function multiRejectExample(){ 
  return new Promise(function (resolve, r         


        

Answer 1

They aren't the same.

Consider the situation where both statements are false. In that case, multiRejectExample() will never reject or resolve the returned promise, whereas tryExample() will "fall through" and resolve the promise automatically (with a value of undefined because you don't return anything).

To demonstrate:

var Promise = require('bluebird');

function test1() {
  return Promise.try(function() { });
}

function test2() {
  return new Promise(function(resolve, reject) { });
}

test1().then(function() { console.log('resolved #1'); });
test2().then(function() { console.log('resolved #2'); });

This will log resolved #1 but not resolved #2 because the promise is never actually resolved (nor rejected).