Node.js async function not being recognized as a valid async function

Question

I've got these 2 functions

async function movieExists(movie){
        return new Promise((resolve, reject) => {
            const sql = '...';

            con.query(sql, (err,result,fields) => {
                if(err)
                    throw err;
                else if(!result[0])
                    reject("Error");
                else
                    resolve(result[0].total);
            })
        })
}

async function addMovie(movie){
        return new Promise((resolve, reject) => {
            const sql = '...';
            const exists = await movieExists(movie); //Error on this line

            if(exists == 0){
                con.query(sql, (err,result,fields) => {
                    if(err)
                        reject("Error");
                    else   
                        resolve("Success");
                })
            }else
                resolve("Movie already exists");
        })
}

Error : SyntaxError: await is only valid in async function

Node version -> v10.16.0

**If you have any suggestions for the code itself I would be glad to hear them.

(resolve, reject) => { that's the function that isn't async ... the fact that it's a promise constructor also suggests you're guilty of the Promise constructor anti-pattern ... you already have something that returns a promise ... you don't need to construct a promise — Jaromanda X
– Jaromanda X, Commented Mar 25, 2020 at 2:22
What is con? Most DB connection libraries on NPM now offer promise-based APIs. Would save you a lot of headache and no more new Promise(... — Phil
– Phil, Commented Mar 25, 2020 at 2:26
I'd actually suggest switching to the musql2 version of your database which has built-in promise support. Then, you can use promises for all your database operations. — jfriend00
– jfriend00, Commented Mar 25, 2020 at 2:43

Kevin Peña · Accepted Answer · 2020-03-25 02:23:32Z

3

The await keyword is directly inside the function that you are passing to new Promise(), which is not async.

Try moving it outside that function, like this:

async function addMovie(movie){
  const exists = await movieExists(movie);
  return new Promise((resolve, reject) => {
    const sql = '...';
    // ...
  })
}

answered Mar 25, 2020 at 2:23

Kevin Peña

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1 Comment

Kevin Peña Over a year ago

On the Promise antipattern others are talking about you might want to look at util.promisify() (added in node 8.0.0)

RBT · Accepted Answer · 2020-03-25 03:31:12Z

1

The second condition is wrong because in the Promise the anonymous function is not async function you can use the following instead, but it is not a good way to control the sequence of async.

async function addMovie(movie){
        return new Promise(async (resolve, reject) => {
            const sql = '...';
            const exists = await movieExists(movie); //Error on this line

            if(exists == 0){
                con.query(sql, (err,result,fields) => {
                    if(err)
                        reject("Error");
                    else   
                        resolve("Success");
                })
            }else
                resolve("Movie already exists");
        })
}

edited Mar 25, 2020 at 3:31

RBT

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answered Mar 25, 2020 at 2:36

zhizhou gu

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