In this post, you learn examples in Nodejs

  • How to pretty print and format json object
  • How to read JSOn object
  • Write json file

How to pretty print jSON object in Nodejs Application

PrettyPrint JSOn is easier to read instead of a normal json string and It contains tabs and spaces.

Pretty printis a way of printing JSON objects with correct indentation, tabs, and spaces and these can be easily read by developers.

This will be very useful for the inspection of a JSON object during debugging.

There are multiple ways we can do it,

Using JSON.stringify method

JSON stringify method Convert the Javascript object to json string by adding the spaces to JSOn string and printing in an easily readable format.

JSOn string contains objects without spaces in employee.json

[{"name":"eric","id":"1"},{"name":"andrew","id":"2"},{"name":"john","id":"3"},{"name":"Flintoff","id":"4"},{"name":"Greg","id":"5"},{"name":"Francis","id":"6"}]

Here is nodejs pretty print example

var fs = require('fs');

fs.readFile('employee.json', 'utf8', function (err, data) {
  if (err) {
    console.log(err);
  } else {
    console.log(JSON.stringify(JSON.parse(data), null, 4));
  }
});

First, Create the native filesystem object fs

  • read the file using readFile, which returns a callback of error and data.
  • returned pretty print json object before parsing json content using JSON object

using prettier npm library

prettier is a code formatter that has support for major programming languages.

First, Install a prettier npm library

npm install prettier --save-dev

Here is a code for Prettier to format json

var jsonData = '{ "active": true, "id": 1, "name": "john" }';
console.log(prettier.format(JSON.stringify(jsonData), { semi: false, parser: "json" }));

How to read external JSON file in Nodejs Application

It is easy to read json data files in Javascript.

There are multiple ways we can achieve it.

using the readFile method to asynchronous read json file

Let’s have an employee.json file that contains the following data.

[
  {
    "name": "eric",
    "id": "1"
  },
  {
    "name": "andrew",
    "id": "2"
  },
  {
    "name": "john",
    "id": "3"
  },
  {
    "name": "Flintoff",
    "id": "4"
  },
  {
    "name": "Greg",
    "id": "5"
  },
  {
    "name": "Francis",
    "id": "6"
  }
]

JSOn files can be parsed in Asynchronous and Synchronous ways.

How to Asynchronous read and parse JSON file here is a readFile example to read the local external JSON file readFile is an asynchronous operation with callback holding err, an error of file read status, data holds the content of the file

var fs = require('fs');


fs.readFile('employee.json', 'utf8', function (err, data) {
  if (err) {
    console.log(err);
  } else {
     console.log(JSON.parse(data));

  }
});

Another way, parse the json file synchronous using require in nodejs.

Here is an user.json file

{ "active": true, "id": 1, "name": "john" }

In Node.js, Import json file using require keyword and It holds the content of the file as a javascript object.

You can access object properties using the object.properties syntax to get the value

var user = require('user.json');
console.log(user.active + ' ' + user.name);

How to Write data to JSOn file in Nodejs Application?

Here is a code for Nodejs write JSON file example

fs module is being used to read and write files from/to a disk.

fs.writeFilewrites a javascript object to json file in an asynchronous way.

var fs = require("fs");
var jsonObj = {
    id: 1,
    name: "Franc"
};

fs.writeFile("./output.json", JSON.stringify(jsonObj, null, 2), (err) => {
    if (err) { console.error(err); return; };
    console.log("Created a JSOn file");
});