Creating .json file and storing data in it with JavaScript?

1- make your obj:

var dict = {"one" : [15, 4.5],
    "two" : [34, 3.3],
    "three" : [67, 5.0],
    "four" : [32, 4.1]};

2- make it JSON:

var dictstring = JSON.stringify(dict);

3- save your json file and dont forget that fs.writeFile(...) requires a third (or fourth) parameter which is a callback function to be invoked when the operation completes.

var fs = require('fs');
fs.writeFile("thing.json", dictstring, function(err, result) {
    if(err) console.log('error', err);
});

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]};