CODEWITHSUNDEEP
javascriptnode.jspromise
Justin
Justin

Reputation: 45320

Node.js promise .then() chaining with defined function

How can I use .then() chaining to call a function that is declared in Node.js? The problem is after the call to getFileType() I want to call getExif() but this is throwing a syntax error:

'use strict';

const FileType = require('file-type');
const exif = require('jpeg-exif');

const path = './alcatraz.jpg';

async function getFileType(filePath) {
    return await FileType.fromFile(filePath);
}

function getExif(filePath) {
    return new Promise((resolve, reject) => {
        exif.parse(filePath, (error, result) => {
            if(error) {
                reject(error);
            } else {
                resolve(result);
            }
        });
    });
}

getFileType(path).then((result) => {
    console.log(result);
})
# ======> problem is here <======
.then(getExif(path) {
    console.log(result);
})
.catch((error) => {
    console.error(error.message);
    process.exit(3);
});

Syntax error is:

SyntaxError: missing ) after argument list

Upvotes: 3

Views: 99

Answers (2)

Nailer
Nailer

Reputation: 36

Maybe you want to do this to get result of getExif.

getFileType(path)
  .then((result) => {
    console.log(result);
  })
  .then(getExif(path)
    .then(resultOfGetExif => console.log(resultOfGetExif))
  )
  .catch((error) => {
    console.error(error.message);
    process.exit(3);
  });

or this just running getExif

getFileType(path)
  .then((result) => {
    console.log(result);
    return result;
  })
  .then((result) => {
    getExif(path)
    console.log(result);
  })
  .catch((error) => {
    console.error(error.message);
    process.exit(3);
  });

I hope these are helpful.

Upvotes: 0

CertainPerformance
CertainPerformance

Reputation: 370629

You should return the call to getExif(path) inside the upper .then, so that the lower .then can consume it:

getFileType(path).then((result) => {
    console.log(result);
    return getExif(path);
})
.then((result) => {
    console.log(result);
})
.catch((error) => {
    console.error(error.message);
    process.exit(3);
});

The result variable in the lower .then will contain the result of calling getExif. If you want both the getFileType and getExif resolve values, since they don't look to depend on each other, use Promise.all instead:

Promise.all([
  getFileType(path),
  getExif(path),
])
  .then(([fileType, exif]) => {
    // work with results
  })
  .catch((error) => {
    console.error(error.message);
    process.exit(3);
  });

Upvotes: 3

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