you can require .json files.

var parsedJSON = require('./file-name');

For example if you have a config.json file in the same directory as your source code file you would use:

var config = require('./config.json');

or (file extension can be omitted):

var config = require('./config');

note that require is synchronous and only reads the file once, following calls return the result from cache

Also note You should only use this for local files under your absolute control, as it potentially executes any code within the file.

You can use JSON.parse().

You should be able to use the JSON object on any ECMAScript 5 compatible JavaScript implementation. And V8, upon which Node.js is built is one of them.

Parsing a string containing JSON data

var str = '{ "name": "John Doe", "age": 42 }';
var obj = JSON.parse(str);

Parsing a file containing JSON data

You'll have to do some file operations with fs module.

Asynchronous version

var fs = require('fs');

fs.readFile('/path/to/file.json', 'utf8', function (err, data) {
    if (err) throw err; // we'll not consider error handling for now
    var obj = JSON.parse(data);
});

Synchronous version

var fs = require('fs');
var json = JSON.parse(fs.readFileSync('/path/to/file.json', 'utf8'));

You wanna use require? Think again!

You can sometimes use require:

var obj = require('path/to/file.json');

But, this is not recommended for several reasons:

1. require will read the file only once. Subsequent calls to require for the same file will return a cached copy. Not a good idea if you want to read a .json file that is continuously updated. You could use a hack. But at this point, it's easier to simply use fs.
2. If your file does not have a .json extension, require will not treat the contents of the file as JSON.
3. require is synchronous. If you have a very big JSON file, it will choke your event loop. You really need to use JSON.parse with fs.readFile.

Seriously! Use JSON.parse.

jsonfile module

If you are reading large number of .json files, (and if you are extremely lazy), it becomes annoying to write boilerplate code every time. You can save some characters by using the jsonfile module.

var jf = require('jsonfile');

Asynchronous version

jf.readFile('/path/to/file.json', function(err, obj) {
  // obj contains JSON data
});

Synchronous version

var obj = jf.readFileSync('/path/to/file.json');

Parsing JSON from streams

If the JSON content is streamed over the network, you need to use a streaming JSON parser. Otherwise it will tie up your processor and choke your event loop until JSON content is fully streamed.

There are plenty of packages available in NPM for this. Choose what's best for you.

Error Handling/Security

If you are unsure if whatever that is passed to JSON.parse() is valid JSON, make sure to enclose the call to JSON.parse() inside a try/catch block. A user provided JSON string could crash your application, and could even lead to security holes. Make sure error handling is done if you parse externally-provided JSON.

use the JSON object:

JSON.parse(str);

Another example of JSON.parse :

var fs = require('fs');
var file = __dirname + '/config.json';

fs.readFile(file, 'utf8', function (err, data) {
  if (err) {
    console.log('Error: ' + err);
    return;
  }

  data = JSON.parse(data);

  console.dir(data);
});

I'd like to mention that there are alternatives to the global JSON object. JSON.parse and JSON.stringify are both synchronous, so if you want to deal with big objects you might want to check out some of the asynchronous JSON modules.

Have a look: https://github.com/joyent/node/wiki/Modules#wiki-parsers-json

Include the node-fs library.

var fs = require("fs");
var file = JSON.parse(fs.readFileSync("./PATH/data.json", "utf8"));

For more info on 'fs' library , refer the documentation at http://nodejs.org/api/fs.html

Since you don't know that your string is actually valid, I would put it first into a try catch. Also since try catch blocks are not optimized by node, i would put the entire thing into another function:

function tryParseJson(str) {
    try {
        return JSON.parse(str);
    } catch (ex) {
        return null;
    }
}

OR in "async style"

function tryParseJson(str, callback) {
    process.nextTick(function () {
      try {
          callback(null, JSON.parse(str));
      } catch (ex) {
          callback(ex)
      }
    })
}

Parsing a JSON stream? Use JSONStream.

var request = require('request')
  , JSONStream = require('JSONStream')

request({url: 'http://isaacs.couchone.com/registry/_all_docs'})
    .pipe(JSONStream.parse('rows.*'))
    .pipe(es.mapSync(function (data) {
      return data
    }))

https://github.com/dominictarr/JSONStream

JSON.parse("your string");

That's all.

as other answers here have mentioned, you probably want to either require a local json file that you know is safe and present, like a configuration file:

var objectFromRequire = require('path/to/my/config.json'); 

or to use the global JSON object to parse a string value into an object:

var stringContainingJson = '\"json that is obtained from somewhere\"';
var objectFromParse = JSON.parse(stringContainingJson);

note that when you require a file the content of that file is evaluated, which introduces a security risk in case it's not a json file but a js file.

here, i've published a demo where you can see both methods and play with them online (the parsing example is in app.js file - then click on the run button and see the result in the terminal): http://staging1.codefresh.io/labs/api/env/json-parse-example

you can modify the code and see the impact...

Everybody here has told about JSON.parse, so I thought of saying something else. There is a great module Connect with many middleware to make development of apps easier and better. One of the middleware is bodyParser. It parses JSON, html-forms and etc. There is also a specific middleware for JSON parsing only noop.

Take a look at the links above, it might be really helpful to you.

My solution:

var fs = require('fs');
var file = __dirname + '/config.json';

fs.readFile(file, 'utf8', function (err, data) {
    if (err) {
        console.log('Error: ' + err);
        return;
    }

    data = JSON.parse(data);

    console.dir(data);
});

Just to make this as complicated as possible, and bring in as many packages as possible...

const fs = require('fs');
const bluebird = require('bluebird');
const _ = require('lodash');
const readTextFile = _.partial(bluebird.promisify(fs.readFile), _, {encoding:'utf8',flag:'r'});
const readJsonFile = filename => readTextFile(filename).then(JSON.parse);

This lets you do:

var dataPromise = readJsonFile("foo.json");
dataPromise.then(console.log);

Or if you're using async/await:

let data = await readJsonFile("foo.json");

The advantage over just using readFileSync is that your Node server can process other requests while the file is being read off disk.

var array={
    Action: 'Login',
    ErrorCode: 3,
    Detail: 'Your account not found.'
};
var http=require('http'),
    PORT=8789,
    server=function(req,res){
        res.writeHead(200,{'Content-Type':'application/json'});

        // JSON
        res.end(JSON.stringify(array));
    }

http.createServer(server).listen(PORT);
console.log('Server started.');

JSON.parse will not ensure safety of json string you are parsing. You should look at a library like json-safe-parse or a similar library.

From json-safe-parse npm page:

JSON.parse is great, but it has one serious flaw in the context of JavaScript: it allows you to override inherited properties. This can become an issue if you are parsing JSON from an untrusted source (eg: a user), and calling functions on it you would expect to exist.

Leverage Lodash's attempt function to return an error object, which you can handle with the isError function.

// Returns an error object on failure
function parseJSON(jsonString) {
   return _.attempt(JSON.parse.bind(null, jsonString));
}


// Example Usage
var goodJson = '{"id":123}';
var badJson = '{id:123}';
var goodResult = parseJSON(goodJson);
var badResult = parseJSON(badJson);

if (_.isError(goodResult)) {
   console.log('goodResult: handle error');
} else {
   console.log('goodResult: continue processing');
}
// > goodResult: continue processing

if (_.isError(badResult)) {
   console.log('badResult: handle error');
} else {
   console.log('badResult: continue processing');
}
// > badResult: handle error

Always be sure to use JSON.parse in try catch block as node always throw an Unexpected Error if you have some corrupted data in your json so use this code instead of simple JSON.Parse

try{
     JSON.parse(data)
}
catch(e){
   throw new Error("data is corrupted")
  }

Just want to complete the answer (as I struggled with it for a while), want to show how to access the json information, this example shows accessing Json Array:

var request = require('request');
request('https://server/run?oper=get_groups_joined_by_user_id&user_id=5111298845048832', function (error, response, body) {
  if (!error && response.statusCode == 200) {
    var jsonArr = JSON.parse(body);
    console.log(jsonArr);
    console.log("group id:" + jsonArr[0].id);
  }
})

If you want to add some comments in your JSON and allow trailing commas you might want use below implemention:

var fs = require('fs');

var data = parseJsData('./message.json');

console.log('[INFO] data:', data);

function parseJsData(filename) {
    var json = fs.readFileSync(filename, 'utf8')
        .replace(/\s*\/\/.+/g, '')
        .replace(/,(\s*\})/g, '}')
    ;
    return JSON.parse(json);
}

Note that it might not work well if you have something like "abc": "foo // bar" in your JSON. So YMMV.

It's simple, you can convert JSON to string using JSON.stringify(json_obj), and convert string to JSON using JSON.parse("your json string").

var fs = require('fs');

fs.readFile('ashish.json',{encoding:'utf8'},function(data,err) {

   if(err) 
      throw err;

   else {

   console.log(data.toString());

 }
})

This had to be shouted at me: it only works for .json files.

If the file ending is different this does not work!