Async/Await is only valid async func while reading a file

Question

I was trying to read a JSON file using Async/Await, I created my example based Native async/await approach, and I got this error.

SyntaxError: await is only valid in async function

Here is my code.

const fs = require('fs-extra');
const xml2js = require('xml2js');  
const parser = new xml2js.Parser();

const path = "file.json";

function parseJM() {
return new Promise(function (resolve, reject) {
    fs.readFile(path, { encoding: 'utf-8'}, (err, data) => {
        if (err) { reject(err); }
        else {
            resolve (parser.parseString(data.replace(/<ent_seq>[0-9]*<\/ent_seq>/g, "")
             .replace(/&(?!(?:apos|quot|[gl]t|amp);|#)/g, '')));
        }
    });
});
}

const var1 = await parseJM();
console.log(var1);

What is wrong with my code? My node version is 11.9.0, my npm version is 6.7.0 and i am using Arch Linux.

What is wrong with my code? ---> await is only valid in async function, like you've already answered in your question — baao, Feb 08 '19 at 12:36
Your using `fs-extra` here, so don't even bother using `new Promise`.. `All fs methods return promises if the callback isn't passed.` — Keith, Feb 08 '19 at 12:42
The purpose of writing like this, the promise is not enough for by itself. — Kaan Taha Köken, Feb 08 '19 at 12:49
I do not understand why the heck this community so harsh on people — Kaan Taha Köken, Feb 08 '19 at 12:53
@KaanTahaKöken As it was noticed, `new Promise` is an antipattern. It's never needed when you have existing promise. — Estus Flask, Feb 08 '19 at 12:54

Shubham · Accepted Answer · 2019-02-11T04:01:41.110

3

You need to call await inside an async function.

(async () => {
    try {
        const var1 = await parseJM();
        console.log(var1);
    } catch (e) {
        console.error(e.message);
    }
})();

Edit: As suggested by @Nik Kyriakides

edited Feb 11 '19 at 04:01

answered Feb 08 '19 at 12:36

Shubham

1,755
3
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`try/catch` is a must when you do this. Otherwise you're setting yourself up for swallowed errors. – nicholaswmin Feb 08 '19 at 12:41
is it possible without using IFFE's – Kaan Taha Köken Feb 08 '19 at 12:44
1

@KaanTahaKöken Yes, you can use a `.then`/`resolve` since `async`-marked functions return a `Promise`. – nicholaswmin Feb 08 '19 at 12:46
@NikKyriakides Not exactly swallowed. You will get `"unhandledRejection"` if an error is thrown inside `parseJM()` call. – Andrei Chernikov Feb 08 '19 at 12:51
@Aikei True, bad choice of words. – nicholaswmin Feb 08 '19 at 12:52

nicholaswmin · Answer 2 · 2019-02-08T12:49:29.283

2

The error itself is telling you exactly what the issue is. You can only await inside an async-marked function.

If that's your top-level code you can just use an async IIFE:

;(async () => {
  try {
    await doSomething()  
  } catch (err) {
    console.error(err)
  }
})()

or just then/catch it. async functions return a Promise after all:

doSomething() 
  .then(result => {
    console.log(result)
  })
  .catch(err => {
    console.error(err)
  })

edited Feb 08 '19 at 12:49

answered Feb 08 '19 at 12:37

nicholaswmin

21,686
15
91
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Why the `;`? Is it a typo or a clever hack I didn't know about? – Nino Filiu Feb 08 '19 at 12:38
1

Just to make sure that you don't fall into [this trap](https://stackoverflow.com/questions/53186265/iife-typeerror-require-is-not-a-function/53186477#53186477). – nicholaswmin Feb 08 '19 at 12:40
That's how code looks when you don't use semi-colons consistently. Not really my thing. – trincot Feb 08 '19 at 12:41
Apart from IIFE's I've *never* had to prefix anything with a `;`. My take is that it's far better w/o them. – nicholaswmin Feb 10 '19 at 05:31

Async/Await is only valid async func while reading a file

2 Answers2