NodeJS File System - node.js

Question

modified an internal JSON file Object property via NodeJS File System through a dropdown on the UI and then when I read it again for further modification, the earlier modified value is not there. When I open the JSON file I can see the modified value but when I read the same file via 'fs.readfile' method, I debug it and I get to see the original value instead of the modified one.
Any suggestions on how to tackle this ?
I am calling this method from the respective place to read the file first and then write to it. This will be called from a separate module.
fileOperation: async function (operation, fileName, dataToWrite) {
switch (operation) {
case 'read':
return new Promise((resolve, reject) => {
fs.readFile(path.join(__dirname, '../../location/' + fileName), function (err, data) {
if (err) {
return reject(err)
} else {
const parsedData= JSON.parse(data);
return resolve(parsedData);
}
})
});
case 'write':
return new Promise((resolve, reject) => {
fs.writeFile(path.join(__dirname, '../../location/' + fileName), JSON.stringify(dataToWrite), {
'Content-Type': 'application/json'
}, function (error) {
if (error) {
return reject(error);
} else {
return resolve('File written successfully');
}
});
})
}
And on the index.js file, this one:
fs.readFile(path.join(__dirname, './location/fileName'), function (err, data) {
if (err) {
res.status(500).send(err);
} else {
fileData = JSON.parse(data).requiredKey;
}
The fileData above is not the one that I saved earlier.
Calling the methods from this switch case:
case 'dropdownSelection':
this.fileOperation('read', 'file.json', {}).then(fileData => {
fileData.key = updatedData;
this.fileOperation('write', 'file.json', fileData).then(success => {
return resolve(success);
}).catch(error => {
return reject(error)
})
}).catch(error => {
return reject(error)
})
break;

Answer 1

There are two likely scenarios I can think of given what you've shared in the question:
1. Timing Issue
It's possible that at the time that you read it again for further modification, the previous modification has yet to complete. File operations take time and are asynchronous, so if you don't handle it correctly, they can happen in an order that you don't expect.
The second code snippet you shared, in index.js, contains a file read. But it's not clear when that code runs. When it runs it will obtain a copy of the file as it was at that time - later updates executed by your dropdown selection will not automatically go back to the index.js unless you initiate another read after the write has completed.
2. Filepath Issue
The filepaths in your code snippets are different. In one case you have path.join(__dirname, '../../location/' + fileName) and in another case you have path.join(__dirname, './location/fileName').
It's possible that your file is writing to a location you aren't expecting. File reads and writes are done relative to current working directory. This means you might inadvertently be reading a different file than you're writing! Try navigating to the folder containing index.js, going up two folders, then into a location folder if one exists, and see if the file you're working with exists there. If it does, you'll know there's a filepath issue.