How to update a value in a json file and save it through node.js

Solution 1:

Doing this asynchronously is quite easy. It's particularly useful if you're concerned with blocking the thread (likely). Otherwise, I'd suggest Peter Lyon's answer

const fs = require('fs');
const fileName = './file.json';
const file = require(fileName);
    
file.key = "new value";
    
fs.writeFile(fileName, JSON.stringify(file), function writeJSON(err) {
  if (err) return console.log(err);
  console.log(JSON.stringify(file));
  console.log('writing to ' + fileName);
});

The caveat is that json is written to the file on one line and not prettified. ex:

{
  "key": "value"
}

will be...

{"key": "value"}

To avoid this, simply add these two extra arguments to JSON.stringify

JSON.stringify(file, null, 2)

null - represents the replacer function. (in this case we don't want to alter the process)

2 - represents the spaces to indent.

Solution 2:

//change the value in the in-memory object
content.val1 = 42;
//Serialize as JSON and Write it to a file
fs.writeFileSync(filename, JSON.stringify(content));