worker Promise support?

Do sheet workers support ES6 Promises? I'm trying to use Promises in a character sheet I'm developing, but even something as simple as the below doesn't seem to work: /**    * Promise-wrapped setAttrs.    */   function _setAttrs(values) {     return new Promise((resolve, reject) => {       setAttrs(values, undefined, () => {         resolve();       });     });   }   on('sheet:opened', () => {     Promise.resolve(42)     .then(value => {       return _setAttrs({         debug: value       });     })     .then(() => {       setAttrs({         debug: 11       });     });   }); The expected behavior is that debug is set to 11 after the sheet is opened. Instead, it gets set to 42, as if it is completely skipping calling the Promise's resolve function in _setAttrs().

In the following mocked-up test I built in the regular API, it works just fine. (() => {   'use strict';   /**    * Promise-wrapped setAttrs.    */   function _setAttrs(values) {     return new Promise((resolve, reject) => {       resolve('this is a test');     });   }   on('ready', () => {     Promise.resolve(42)     .then(value => {       return _setAttrs({         debug: value       });     })     .then(value => {       log(value);       return _setAttrs({         debug: 11       });     })     .catch(err => {       _setAttrs({         debug: err.toString()       });     });   }); })(); Here, the Promises get resolved and 'this is a test' is printed to the API log, as expected. The mocked-up test works fine in the web worker if I replace the 'ready' event with 'sheet:opened' and do setAttrs({debug: value}) instead of log(value). So it looks like the Promise implementation isn't the culprit. Maybe I've found a bug in setAttrs' callback?

It may simply be that sheet workers and the API are running different engines, where one has Promise support and the other doesn't.