Cleanest way to use async results in Javascript

Question

Coming from C++ and Python, I still struggle with Javascript asynchronous ubiquity. Sometimes it's very useful, but other times I just don't see how to fit it in without writing terrible code.

I have a Node.js + Express CRUD setup, and I have to do some basic check-ups before continuing with the request. I want to check that http POST fields match with database fields before running the final query. I cannot declare it an async function and use await as it must match a given Interface.

showColumns(dbTable) returns a db premise with a SHOW COLUMNS query.

The only solution that I found is:

database.showColumns(dbTable).then((columns)=>{

  //But do I really need to put all my logic inside a then???

  let row =  Object.keys(req.body).filter({}.hasOwnProperty.bind(columns));
  //... all the rest of the logic goes here

});

In your opinion, what is the cleanest/most elegant way to solve that?

You can put all your logic inside an Async IIFE, like so: (async () =>{ /** your code **/ })(); — Luca Kiebel
– Luca Kiebel, Commented Aug 7, 2018 at 12:07

justMe · Accepted Answer · 2018-08-07 12:07:51Z

3

database.showColumns(dbTable)
  .then(columns => this.handleColumns(columns))
  .then(parsedData => this.doSthElse(parsedData);

You can extract your logic to a seperate method. However, it must be called inside then as it is the callback triggered once your async operation is finished.

Alternatively, you might consider using generators, async/await functions or promises.

answered Aug 7, 2018 at 12:07

justMe

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2 Comments

Duccio Over a year ago

I find no point in splitting the code into multiple .then when there are only two async calls, and the latter solves the whole Premise. If you have a few single async functions to call, a chain of .then is nice and readable. But I don't believe that a long function with some more logic is more readable inside multiple .then()

justMe Over a year ago

Splitting into multiple then's makes sence if each one of them does a different asynchronous operation. My snippet was an example of how you can chain multiple async calls. Every then returns a promise.

Nishant Dixit · Accepted Answer · 2018-08-07 12:10:22Z

1

You can use async/await for this.

(async function() {
    try {
        var columns = await database.showColumns(dbTable)
        let row = Object.keys(req.body).filter({}.hasOwnProperty.bind(columns));
    } catch (e) {
        console.log("Promise error");
    }
})

answered Aug 7, 2018 at 12:10

Nishant Dixit

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2 Comments

Duccio Over a year ago

Clever! It's definitely more readable than the .then, as the whole function can be wrapped without breaking it in the middle. Of course I assume it needs the "();" at the end to execute

Nishant Dixit Over a year ago

You don't need to wrap function with "()" I did just because of I am defining anonymous function here You can remove if you are defining actual function with name.

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