Kevin Le

Posted on Dec 31, 2017

Modernize your ReactJS application with async/await in 2018

#react #asyncawait

To start 2018, you can modernize your ReactJS application by incorporating the async/await feature. Assume you already use a Promise-based HTTP client library such as axios, you can easily refactor your existing code, or you can just start using async/await in new codes.

Either way or both, here's a small snippet that can help:

import axios from 'axios';
...
class Login extends Component {
    constructor(props, context) {
        super(props, context);
        this.onLogin = this.onLogin.bind(this);
        ...
    }
    async onLogin() {
        const { email, password } = this.state;
        try {
            const response = await axios.post('/login', { email, password });
            console.log(response);
        } catch (err) {
            //handle error
        }
    }
    ...
}

So the code change is very minimal. But running webpack might result in an error. The error might say something like regeneratorRuntime is not defined. In that case, it's a simple fix:

npm install babel-plugin-transform-runtime --save-dev

Then in the .babelrc file, simply add

{
    ...
    "plugins": [
        ["transform-runtime", {
            "regenerator": true
        }]
    ]
}

Other than adding babel-plugin-transform-runtime and a simple modification to the .babelrc file, no babel-runtime, no polyfill is necessary.

Top comments (4)

Dominik Weber • Jan 5 '18

Did you have a look at the transpiled JS code?

While async/await is a great feature, the size of the transpiled code is enormous.

The simple onLogin method of your example gets transpiled to this:

var onLogin = function () {
    var _ref = _asyncToGenerator( /*#__PURE__*/regeneratorRuntime.mark(function _callee() {
        var _state, email, password, response;

        return regeneratorRuntime.wrap(function _callee$(_context) {
            while (1) {
                switch (_context.prev = _context.next) {
                    case 0:
                        _state = undefined.state, email = _state.email, password = _state.password;
                        _context.prev = 1;
                        _context.next = 4;
                        return axios.post('/login', { email: email, password: password });

                    case 4:
                        response = _context.sent;

                        console.log(response);
                        _context.next = 10;
                        break;

                    case 8:
                        _context.prev = 8;
                        _context.t0 = _context['catch'](1);

                    case 10:
                    case 'end':
                        return _context.stop();
                }
            }
        }, _callee, undefined, [[1, 8]]);
    }));

    return function onLogin() {
        return _ref.apply(this, arguments);
    };
}();

So before using async/await, one should ask if the increased code size is acceptable.

Kevin Le • Jan 10 '18

It's good to have an eye on the transpiled code. For a simple case, it might seem like there's no gain of using async/await over using then clauses. But the benefits of using async/await will be more obvious when the business logic gets more complicated. Async/await code will be more readable than "then" clauses.

Now if you have to stop each time to compare the size of the transpiled code, then I recommend against that. I also recommend against coming up with a rule that says something like "Ok, less than 2 "then" clauses, then no async/await".
Business logic does change. So suddenly we have to make one more asynchronous call, then such rule is more trouble than it's worth.

Nick Taylor • Jan 26 '18

It depends what browsers you're targeting. Assuming (and I hope) you use babel-preset-env, async/await will only be transpiled to ES5 for pretty much just IE11 and below. All the other browsers support await now.

If most of your market is IE <= 11 , then maybe perhaps it's not wise to use async/await. Honestly though so many things come in to play for bundle size, but obviously a smaller bundle size is usually a good thing.

Dominik Weber • Jan 28 '18

This is great news! Since it's ES7 I assumed it won't be implemented by browsers yet.

Thanks for pointing out that it is.

Regarding the bundle size, I agree that many things affect that. But I don't think that bloating up async/await statements to 10x the original code size is negligible.

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Modernize your ReactJS application with async/await in 2018

Top comments (4)

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