Encountering an async issue with npm exiftool in JavaScript

Question

Encountering an async issue with npm exiftool in JavaScript

I'm facing issues with npm exiftool usage. (https://www.npmjs.com/package/exiftool) I'm attempting to perform some tasks using it.

Iterate through image files in a specific folder
Retrieve 'xpKeywords' data of each image file
Write the file storing data

Below is my code snippet.

const fs = require('fs');
const exif = require('exiftool');
const folderName = 'testImages';
const inputPath = `/Users/myName/Project/project/${folderName}`;
const files = fs.readdirSync(inputPath, 'utf8');

let data = [];

(async () => {
  let promises = [];
  files.forEach(file => promises.push(fs.readFileSync(`${inputPath}/${file}`)));
  let results = await Promise.all(promises);
  for(let [index, result] of results.entries()) {
    let datum = await getMetadata(result, index);
    console.log("out");
    data.push(datum);
  }
  fs.writeFileSync('outputData/metaData.json', JSON.stringify(data, null, 4), (error) => {
    console.log('Error Occurred');
  });
})();

async function getMetadata(result, index) {
  console.log(`get metadata ${index}`);
  await exif.metadata(result, (err, metadata) => {
    return {
      name: files[index],
      hashTags: metadata.xpKeywords
    };
  });
}

Upon executing this code, the generated metaData.json file does not match my expectations.

[ null, null, null, null, null, null ]

I suspect there might be an issue with the use of async functions within the getMetadata function.

javascript npm exiftool

Answer 1

Answer №1

There seems to be a few issues in your code.

The main problem is that the function getMetaData does not return any value. Simply returning from the callback passed to exif.metadata does not set the return value of getMetaData.
Additionally, fs.readFileSync does not return a promise, so using
```
let results = await Promise.all(promises);
```
serves no purpose as it operates synchronously.
Accessing files via indexes in a module global variable can lead to errors.

To handle promises effectively, consider utilizing Node.js's experimental file promises API, or apply util.promisify on fs.readFile for asynchronous functionality. You can also use promisify on exif.metadata to work with promises.

For detailed information on converting callback-based APIs to promises, refer to this question's answers.

In light of these considerations, here's a modified version of your code (may require adjustments):

const fs = require('fs');
const {promisify} = require('util');
const exif = require('exiftool');

const pReaddir = promisify(fs.readdir);
const pReadFile = promisify(fs.readFile);
const pWriteFile = promisify(fs.writeFile);
const pMetadata = promisify(exif.metadata);

const folderName = 'testImages';
const inputPath = `/Users/myName/Project/project/${folderName}`;

(async () => {
    // Retrieve file names
    const files = await pReaddir(inputPath, 'utf8');
    // Process files concurrently and wait for the result
    const data = Promise.all(files.map(async(name) => {
        // Read the file and extract metadata
        let {xpKeywords: hashTags} = await pMetadata(await pReadFile(`${inputPath}/${name}`));
        // Construct an object with the filename and xpKeywords as hashTags
        return {name, hashTags};
    }));
    // Save the results to a file
    await pWriteFile('outputData/metaData.json', JSON.stringify(data, null, 4));
})()
.catch(error => {
    console.error(error);
});

Answer 2

There seems to be a few issues in your code.

The main problem is that the function getMetaData does not return any value. Simply returning from the callback passed to exif.metadata does not set the return value of getMetaData.
Additionally, fs.readFileSync does not return a promise, so using
```
let results = await Promise.all(promises);
```
serves no purpose as it operates synchronously.
Accessing files via indexes in a module global variable can lead to errors.

To handle promises effectively, consider utilizing Node.js's experimental file promises API, or apply util.promisify on fs.readFile for asynchronous functionality. You can also use promisify on exif.metadata to work with promises.

For detailed information on converting callback-based APIs to promises, refer to this question's answers.

In light of these considerations, here's a modified version of your code (may require adjustments):

const fs = require('fs');
const {promisify} = require('util');
const exif = require('exiftool');

const pReaddir = promisify(fs.readdir);
const pReadFile = promisify(fs.readFile);
const pWriteFile = promisify(fs.writeFile);
const pMetadata = promisify(exif.metadata);

const folderName = 'testImages';
const inputPath = `/Users/myName/Project/project/${folderName}`;

(async () => {
    // Retrieve file names
    const files = await pReaddir(inputPath, 'utf8');
    // Process files concurrently and wait for the result
    const data = Promise.all(files.map(async(name) => {
        // Read the file and extract metadata
        let {xpKeywords: hashTags} = await pMetadata(await pReadFile(`${inputPath}/${name}`));
        // Construct an object with the filename and xpKeywords as hashTags
        return {name, hashTags};
    }));
    // Save the results to a file
    await pWriteFile('outputData/metaData.json', JSON.stringify(data, null, 4));
})()
.catch(error => {
    console.error(error);
});

Encountering an async issue with npm exiftool in JavaScript

Answer №1

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