DevGrok

There isn't support for  async iterators ( for await...of ) in Node.js v8.9 which is AWS Lambda's runtime. It's shame, as it’s a great feature that allows you to iterate over an iterable that returns as result asynchronously, i.e. retrieving another page from a database, using a compact for loop that feels synchronous but under the covers is actually done asynchronously. Which means, if you want to use a library that written specifically to use it (e.g.  Amazon DynamoDB QueryPaginator ), you have to use an even more verbose syntax. However with a bit of re-purposing you can use a generator function that returns a Promise and if you await each promise given in the loop it will behave like an async iterator.

Node.js uses async functions extensively, as it based around non-blocking I/O. Each function takes a callback function parameter, which can result in some messy, deeply nested callback functions if you have to call a bunch of async functions in sequence. Promises make these callbacks a lot cleaner. ES6 (or ES2016)  Promise s are a great way of chaining together asynchronous functions so that they read like a series of synchronous statements. There's already some great posts on Promises, 2ality has a good intro to async then detail of the api , so I won't rehash that article. However, after starting to use them for cases more complicated than most examples, it easy to make a few mistaken assumptions or make things difficult for yourself. So here is a more complicated example showing a pattern I like to follow. In this example, I'll use the new Javascript Fetch API , which is an API that returns a Promise, allowing you to make async HTTP calls without having to muck a...