JavaScript Promise Examples

promise_examples.js

//1.
new Promise(function(resolve, reject) {
  console.log('A');
  resolve();
}).then(function() {
  console.log('B');
});
console.log('C');
//A, C, B

//2.
function ajax(options) {
  return new Promise(function(resolve, reject) {
    jQuery.ajax(options).done(resolve).fail(reject);
  });
}
console.log('A');
ajax({ url: '/' }).then(function(result) {
  console.log(result.length);
  console.log('B');
});
console.log('C');

//3.
console.log('A');
new Promise(function(resolve, reject) {
  jQuery.ajax({ url: '/' }).done(resolve).fail(reject);
}).then(function(result) {
  console.log(result.length);
  console.log('B');
});
console.log('C');

Source:
https://www.stephanboyer.com/post/107/fun-with-promises-in-javascript
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise