How to run Node.js app with ES2017 features enabled on Heroku?
Specify the node version you want to use in your package.json: https://devcenter.heroku.com/articles/nodejs-support#specifying-a-node-js-version
So for async/await support you'll want to specify >= 7.6.0
{ "engines": { "node": ">= 7.6.0" }}
From the Heroku documentation here
https://devcenter.heroku.com/articles/getting-started-with-nodejs#declare-app-dependencies
it should be declared in your package.json file which engine(s) should be accessible:
{ "name": "node-js-getting-started", "version": "0.2.5", ... "engines": { "node": "5.9.1" }, "dependencies": { "ejs": "2.4.1", "express": "4.13.3" }, ...}