CODEWITHSUNDEEP
javascriptnode.jsexpresskoakoa2
Saitama
Saitama

Reputation: 497

koa: promise vs async await middleware

I'm trying to write a Koa middleware, if condition met, go to next middelware. If condition unmet, short-circuit the flow. I found 2 ways, using promise or async/await.

Method 1: Promise-based 

app.use(function(ctx, next){
    // if condition met 
    if (conditionMet){
        ctx.somedata = 'bar';
        // go to next middleware
        return next();
    }
})

Method 2: Async/Await 

app.use(async function(ctx, next){
    // if condition met 
    if (conditionMet){
        ctx.somedata = 'bar';
        // go to next middleware
        await next();
    }
})

Is there any difference between these 2 methods? If there's not any, which one is preferred?

Upvotes: 1

Views: 1858

Answers (1)

Javier Aviles
Javier Aviles

Reputation: 10695

When there's no code after await next(), you achieve the same thing. As ippi mentioned in the comment, when having code afterwards, with await will just be "cleaner" as it will wait until the promise is resolve to go to next line, while in the "common promises way" you would have to handle the resolution of the promise. In your specific example, it doesn't matter, but probably in other parts of your code you will use one or the other (maybe in another middleware?), and you will want to homogenize your code.

In case you would have something afterwards you would do it this way (probably you already know):

async functions (node v7.6+)

app.use(async (ctx, next) => {
    // if condition met 
    if (conditionMet){
        ctx.somedata = 'bar';
        // go to next middleware
        await next();
        // after code
        console.log('this will be executed after promise next() is resolved');
    }
});

Common function

app.use((ctx, next) => {
    // if condition met 
    if (conditionMet){
        ctx.somedata = 'bar';
        // go to next middleware
        return next().then(() => {
            // after code
            console.log('this will be executed after promise next() is resolved');
        });
      }
});

I cannot say there is a better one, they are just different. For me async/await looks clenaer and I can personally control better the flow of the code and avoid Promises Hell. I think they are getting stronger and supported by the new javascript standard but for someone that started coding with js maybe original promises looks better...

Upvotes: 2

Related Questions