This is a simple way to update (or load) a JSON file. If the JSON file does not exist it will be created (along with a directory structure if those directories don't exist yet).

Uses underscore to extend existing JSON data with the object you specify, overriding anything with an existing property and adding properties if they are new.

NEW: You may change the extend behavior by calling config({deep:true}) before calling update. This will use deep-extend instead of underscore extend to merge the data when you call update.

New version supports promises (and async/await with babel).

npm install json-update

Updating a JSON file (and return the new object) (with promise):

json = require('json-update');

json.update('data.json',{test:10})
.then(function(dat) { 
  console.log(dat.test) 
});

With async/await (you must use babel with babel-polyfill etc. as with all use of async/await):

import {update, load} from 'json-update';

async function test() {
  await update('t.json', {x:2});
  let dat = await load('t.json');
  console.log(dat.x);
}

test().then(()=> {}).catch( e=> {console.error(e)}); 

With a callback:

json = require('json-update')

json.update('data.json', { test: 'value x' }, function(err, obj) {
  if (typeof err !== "undefined" && err !== null) {
    console.log("Error updating json: " + err.message);
  }
  console.log(obj);
});

Loading a JSON file (note that in the case of loading a valid JSON file must already exist):

json = require('json-update')

json.load('data.json', function(err, obj) {
  console.log("Loaded from json:");
  console.log(obj);
});