Async in 2017 made easy

André Werlang (@awerlang)

Node.js

source: https://nodejs.org/en/

LTS schedule

source: https://github.com/nodejs/LTS#lts-schedule

Node.js ES2017 support

source: http://node.green/

Node.js ES2017 support

To clarify, async/await is not yet finished. I'm working on fixing bugs and writing tests. If 53 branched today, we would not turn on the async/await flag on. I would not recommend using experimental features in production--they are often behind flags because they are not working 100% correctly. -- @littledan

source: https://github.com/nodejs/promises/issues/4

TC-39

promises - the old new way


function chainAnimationsPromise(elem, animations) {
    let ret = null;
    let p = currentPromise;
    for(const anim of animations) {
        p = p.then(function(val) {
            ret = val;
            return anim(elem);
        })
    }
    return p.catch(function(e) {
        /* ignore and keep going */
    }).then(function() {
        return ret;
    });
}

*deprecated, in JavaScript standards

(just kidding)

source: https://tc39.github.io/ecmascript-asyncawait/

enters async functions


async function chainAnimationsAsync(elem, animations) {
    let ret = null;
    try {
        for(const anim of animations) {
            ret = await anim(elem);
        }
    } catch(e) { /* ignore and keep going */ }
    return ret;
}

source: https://tc39.github.io/ecmascript-asyncawait/

serialization


async function downloadAll(urls) {
    const list = [];
    for (const url of urls) {
        const ret = await fetch(url);
        list.push(ret);
    }
    return list;
}

chart

serial timeline

concurrency


async function downloadAll(urls) {
    const list = [];
    for (const url of urls) {
        const ret = fetch(url);
        list.push(ret);
    }
    return await Promise.all(list);
}

concurrency (2)


async function downloadAll(urls) {
    return await Promise.all(urls.map(url => fetch(url)));
}

chart

concurrent timeline

express routes


app.get('/', (req, res) => {
    service.get(req)
        .then(data => {
            res.send(data)
        })
        .catch(() => {
            res.send(500, 'Oops...')
        })
})

express routes with async


app.get('/', async (req, res) => {
    try {
        const data = await service.get(req)
        res.send(data)
    } catch (e) {
        res.send(500, 'Oops...')
    }
})

express routes with async (2)


app.get('/', async (req, res) => {
    const data = await service.get(req)
    res.send(data)
})

express wrap() helper


function wrap(fn) {
    return (req, res, next) => {
        const maybe_promise = fn(req, res, next);
        if (maybe_promise && typeof maybe_promise.catch === 'function') {
            maybe_promise.catch(next);
        }
    };
}

app.get('/', wrap(async (req, res) => {
    const data = await service.get(req)
    res.send(data)
}))

express monkey patch

I'm not always monkeypatching. But when i do it's Promise support for express.
-- @garkin

express monkey patch (2)


var Layer = require("express/lib/router/layer");
Layer.prototype.handle_request = function handle(req, res, next) {
    var fn = this.handle;
    if (fn.length > 3) return next();
    try {
        var maybe_promise = fn(req, res, next);
        if (maybe_promise && typeof maybe_promise.catch === "function") {
            maybe_promise.catch(next);
        }
    } catch (err) {
        next(err);
    }
};

source: https://gist.github.com/garkin/39e55d74c486cd75141d3d6721091cb2

express middlewares

  • Beware async functions ain't supported in middlewares

other considerations

  • interoperability
  • exception handling

node v7

node --harmony-async-await

babel setup

Node >= v6

npm install --save-dev babel-preset-es2017

.babelrc:


{
  "presets": [
    "es2017"
  ]
}

try: babel repl

babel setup (2)

Alternatively:

npm install --save-dev babel-plugin-transform-async-to-generator

.babelrc:


{
  "plugins": [
    "transform-async-to-generator"
  ]
}

TypeScript

  • TypeScript 1.7: targets ES6
  • typescript@next: targets both ES5 and ES3

async function downloadAll(urls: string[]): Promise<any[]> {
    return await Promise.all(urls.map(url => fetch(url)));
}

try: https://www.typescriptlang.org/play/index.html

references

  • https://tc39.github.io/ecmascript-asyncawait/
  • https://github.com/expressjs/express/pull/2809
  • https://strongloop.com/strongblog/async-error-handling-expressjs-es7-promises-generators/
  • https://blog.risingstack.com/async-await-node-js-7-nightly/