How to parse JSON using Node.js? [closed]

Answer 1

I use fs-extra. I like it a lot because -although it supports callbacks- it also supports Promises. So it just enables me to write my code in a much more readable way:

const fs = require('fs-extra');
fs.readJson("path/to/foo.json").then(obj => {
    //Do dome stuff with obj
})
.catch(err => {
    console.error(err);
});

It also has many useful methods which do not come along with the standard fs module and, on top of that, it also bridges the methods from the native fs module and promisifies them.

NOTE: You can still use the native Node.js methods. They are promisified and copied over to fs-extra. See notes on fs.read() & fs.write()

So it's basically all advantages. I hope others find this useful.

Answer 2

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.

Note: If you're using a JSON file to store sensitive information (e.g. passwords), that's the wrong way to do it. See how Heroku does it: https://devcenter.heroku.com/articles/config-vars#setting-up-config-vars-for-a-deployed-application. Find out how your platform does it, and use process.env to retrieve the config vars from within the code.

---

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, I do not recommend this for several reasons:

1. 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.
2. 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.
3. If your file does not have a .json extension, require will not treat the contents of the file as JSON.

Seriously! Use JSON.parse.

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load-json-file 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 load-json-file module.

const loadJsonFile = require('load-json-file');

Asynchronous version

loadJsonFile('/path/to/file.json').then(json => {
    // `json` contains the parsed object
});

Synchronous version

let obj = loadJsonFile.sync('/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.

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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.

Answer 3

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.

Answer 4

If the JSON source file is pretty big, may want to consider the asynchronous route via native async / await approach with Node.js 8.0 as follows

const fs = require('fs')

const fsReadFile = (fileName) => {
    fileName = `${__dirname}/${fileName}`
    return new Promise((resolve, reject) => {
        fs.readFile(fileName, 'utf8', (error, data) => {
            if (!error && data) {
                resolve(data)
            } else {
                reject(error);
            }
        });
    })
}

async function parseJSON(fileName) {
    try {
        return JSON.parse(await fsReadFile(fileName));
    } catch (err) {
        return { Error: `Something has gone wrong: ${err}` };
    }
}

parseJSON('veryBigFile.json')
    .then(res => console.log(res))
    .catch(err => console.log(err))

Answer 5

Use this to be on the safe side

var data = JSON.parse(Buffer.concat(arr).toString());

Answer 6

NodeJs is a JavaScript based server, so you can do the way you do that in pure JavaScript...

Imagine you have this Json in NodeJs...

var details = '{ "name": "Alireza Dezfoolian", "netWorth": "$0" }';
var obj = JSON.parse(details);

And you can do above to get a parsed version of your json...