I have a back-end JavaScript file that runs on node.js. It do some stuff using async.series and yields the final dictionary(object) with data I need on my front-end. I now how to read a .json file and convert it into the JavaScript object, but I do not know create .json file with back-end JavaScript and how to store some data in it. 
Could anyone please tell me the right way to do this.
Here is the dictionary(object) that I need to convert and store to the .json file.
var dict = {"one" : [15, 4.5],
            "two" : [34, 3.3],
            "three" : [67, 5.0],
            "four" : [32, 4.1]};
				
				Simple! You can convert it to a JSON (as a string).
    var dictstring = JSON.stringify(dict);
To save a file in NodeJS:
    var fs = require('fs');
    fs.writeFile("thing.json", dictstring);
Also, objects in javascript use colons, not equals: 
    var dict = {"one" : [15, 4.5],
            "two" : [34, 3.3],
            "three" : [67, 5.0],
            "four" : [32, 4.1]};