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

Question

How do I update a value in a json file and save it through node.js? I have the file content:

var file_content = fs.readFileSync(filename); var content = JSON.parse(file_content); var val1 = content.val1; 

Now I want to change the value of val1 and save it to the file.

Answer 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.

Answer 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));