Livecoding: JavaScript Async/Await and Morty's Mindblowers [Video]

This Sunday, I created an excuse to learn JavaScript async/await: Morty's Mindblowers.

Async/await is meant to be the bestest way to deal with asynchronous code in JavaScript. Even better than promises. And since the web is littered with async/await tutorials, it must be really hard, right?

No... just like Promises, it's nothing but a monad. A nice syntax sugarified monad, but still a monad. You can learn how to use async/await in 10 seconds.

Watch. Read.

If you know Promises, you know async/await. Congratz!

Let's say you want to fetch a list of images from Imgur and narrow it down to videos. With Promises, it looks like this:

class Imgur {
    static URL = 'https://api.imgur.com/3/' ;
    static CLIENT_ID = 'c848e36012571f2' ;

    static gifs(page) {
         return fetch(`${Imgur.URL }gallery/hot/rising/${page}`,
                     {headers: { Authorization: `Client-ID ${Imgur.CLIENT_ID }`} }
        ).then (res => res.json ( ) )
         .then (json => {
             if (json.success ) {
                 return json.data.filter ( ( { type } ) => type === 'video/mp4' ) ;
             } else {
                 throw new Error(json.data.error ) ;
             }
         } )
    }
}

We have a static gifs() method that uses fetch to talk to Imgur and return a Promise. The promise resolves with either a list of Imgur videos, or it rejects with an API error.

Using static lets us call this API without instantiating an object. Imgur.gifs() for instance. Great for when you're using classes to group stuff and don't need objects.

Ok, so this code is pretty readable, right? Fetch data, then parse it, then do things.

With async/await, that same code looks like this:

class Imgur {
    static URL = 'https://api.imgur.com/3/' ;
    static CLIENT_ID = '<your_id>' ;

    static async gifs(page) {
        const res = await fetch(`${Imgur.URL }gallery/hot/rising/${page}`,
                                {headers: { Authorization: `Client-ID ${Imgur.CLIENT_ID }`} } ) ,
              json = await res.json ( ) ;

        if (json.success ) {
            return json.data.filter ( ( { type } ) => type === 'video/mp4' ) ;
        } else {
            throw new Error(json.data.error ) ;
        }
    }
}

I don't know if that's more readable, but I can see the appeal. Your code looks just like any other code. No need to think about async stuff at all.

You have to put async in front of your function name. That wraps it in a Promise. Anything you return is in a Promise monad. Time bubble to use the metaphor from my JavaScript Promises in 2 minutes article.

You peek into that monad using the await keyword. It's like wrapping your code in a .then callback.

That's really all there is to it. Once you say json = await res.json(), anything that uses that json variable gets wrapped in a .then() call.

Any time you use the Imgur.gifs() method, you have to say await and your function must be wrapped in async.

Oh, and you can wrap built-in React lifecycle hooks in async and it works as expected. That part is neat. However, you can't have async getters. That would be cool.

So yeah, we got the JavaScript async/await stuff working in a couple minutes, then we spent some half an hour figuring out how Imgur's API works, and an hour or two trying to use flexbox to make the <video> tag shrink and grow.

And in the end, we got Morty's Mindblowers. It uses cut scenes from an episode of Rick & Morty to show you random gifs from Imgur's front page.

Enjoy!