Node.js Tutorial - Node.js NPM JSON

NPM uses JSON files for configuring modules.

JSON is a standard format transfer data over the network.

JSON is a subset of JavaScript object literals.

For JSON you must use quotation marks for JavaScript object keys.

JSON limits a value for a given key.

The values can only be a string, number, boolean (true or false), array, null, or another valid JSON object.


The following code shows a valid JSON object.

    "firstName": "CSS", 
    "lastName": "HTML", 
    "isAlive": true, 
    "age": 5, 
    "height_cm": 111.12, 
    "address": {
         "streetAddress": "1234 Main Street", 
         "city": "New York", 
         "state": "NY",
    "phoneNumbers": [ 
        { "type": "home", "number": "222 555-1234" }, 
        { "type": "fax", "number": "666 555-4567" }
    "additionalInfo": null 

The firstName value is a string, age is a number, isAlive is a boolean, phoneNumbers is an array of valid JSON objects, additionalInfo is null, and address is another valid JSON object.

The last property in JSON must not have an extra comma.

Loading JSON in Node.js

We can load a JSON object from the file system the same way we load a JavaScript module.

Every single time within the module loading sequence, if a file.js is not found, Node.js looks for a file.json.

If it is found, it returns a JavaScript object representing the JSON object.

In the c:/json/filebased/config.js we have

   "myData": "this is the value for myData" 

The following code uses require to load JSON data.

var config = require('./config'); 
console.log(config.myData); // this is the value for myData 

JSON Converter

JSON object has functions for converting a string representation of JSON to JavaScript objects and converting JavaScript objects into a JSON string.

To convert a JavaScript object to a JSON string, call JSON.stringify passing in the JavaScript object.

This function returns the JSON string representation of the JavaScript object.

To convert a JSON string into a JavaScript object, use the JSON.parse function, which simply parses the JSON string and returns a JavaScript object.

var myData = {
    a: 1, // ww w .j a  v a  2s.  c  o  m
    b: 'a string', 
    c: true 
// convert a JavaScript object to a string 
var json = JSON.stringify(myData); 
console.log(typeof json); // string 

// convert a JSON string to a JavaScript object 
var backToJs = JSON.parse(json); 
console.log(backToJs.a); // 1 

The code above generates the following result.