How to parse JSON using Node js

Question

How should I parse JSON using Node js  Is there some module which will validate and parse JSON securely

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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

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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

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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

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Use this to be on the safe side  var data   JSON parse Buffer concat arr  toString

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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   gt          Do dome stuff with obj     catch err   gt        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    amp  fs write      So it s basically all advantages  I hope others find this useful

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Use JSON parse str    Read more about it here   Here are some examples   var jsonStr      result  true   count  42     obj   JSON parse jsonStr    console log obj count         expected output  42 console log obj result        expected output  true

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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    gt        fileName        dirname    fileName       return new Promise  resolve  reject    gt            fs readFile fileName   utf8    error  data    gt                if   error  amp  amp  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   gt  console log res        catch err   gt  console log err

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You can use JSON parse    which is a built in function that will probably force you to wrap it with try-catch statements    Or use some JSON parsing npm library  something like json-parse-or

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If you need to parse JSON with Node js in a secure way  aka  the user can input data  or a public API  I would suggest using secure-json-parse   The usage is like the default JSON parse but it will protect your code from    prototype poisoning  and constructor abuse    const badJson       a   5   b   6     proto        x   7     constructor     prototype     bar    baz         const infected   JSON parse badJson  console log infected x     print undefined  const x   Object assign     infected  console log x x     print 7  const sjson   require  secure-json-parse   console log sjson parse badJson      it will throw by default  you can ignore malicious data also

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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

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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    x000D   x000D  var request   require  request    x000D  request  https   server run oper get groups joined by user id amp user id 5111298845048832   function  error  response  body    x000D    if   error  amp  amp  response statusCode    200    x000D      var jsonArr   JSON parse body   x000D      console log jsonArr   x000D      console log  group id     jsonArr 0  id   x000D      x000D     x000D   x000D   x000D

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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   gt  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

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var fs   require  fs     fs readFile  ashish json   encoding  utf8   function data err        if err         throw err      else       console log data toString

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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

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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

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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

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You can simply use JSON parse    The definition of the JSON object is part of the ECMAScript 5 specification  node js is built on Google Chrome s V8 engine  which adheres to ECMA standard  Therefore  node js also has a global object JSON docs     Note - JSON parse can tie up the current thread because it is a synchronous method  So if you are planning to parse big JSON objects use a streaming json parser

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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

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No further modules need to be required  Just use var parsedObj   JSON parse yourObj   I don think there is any security issues regarding this

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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

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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

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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

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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

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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    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  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  If your file does not have a  json extension  require will not treat the contents of the file as JSON    Seriously  Use JSON parse     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   gt            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     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

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As mentioned in the above answers  We can use JSON parse   to parse the strings to JSON But before parsing  be sure to parse the correct data or else it might bring your whole application down  it is safe to use it like this  let parsedObj      try       parsedObj   JSON parse data     catch e        console log  Cannot parse because data is not is proper json format

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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

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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

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Using JSON for your configuration with Node js  Read this and get your configuration skills over 9000        Note  People claiming that data   require    data json    is a   security risk and downvoting people s answers with zealous zeal  You re exactly and completely wrong    Try placing non-JSON in that file    Node will give you an error  exactly like it would if you did the same thing with the much slower and harder to code manual file read and then subsequent JSON parse     Please stop spreading misinformation  you re hurting the world  not helping   Node was designed to allow this  it is not a security risk    Proper applications come in 3  layers of configuration    Server Container config Application config  optional  Tenant Community Organization config User config   Most developers treat their server and app config as if it can change   It can t   You can layer changes from higher layers on top of each other  but you re modifying base requirements  Some things need to exist   Make your config act like it s immutable  because some of it basically is  just like your source code   Failing to see that lots of your stuff isn t going to change after startup leads to anti-patterns like littering your config loading with try catch blocks  and pretending you can continue without your properly setup application   You can t  If you can  that belongs in the community user config layer  not the server app config layer   You re just doing it wrong   The optional stuff should be layered on top when the application finishes it s bootstrap   Stop banging your head against the wall  Your config should be ultra simple   Take a look at how easy it is to setup something as complex as a protocol-agnostic and datasource-agnostic service framework using a simple json config file and simple app js file     container-config js            service              type      http            name      login            port     8085             data              type      mysql            host      localhost            user      notRoot            pass      oober1337            name      connect            index js     the engine that powers everything   var config        require    container-config json             Get our service configuration  var data          require config data type                 Load our data source plugin   npm install mysql  for mysql   var service       require config service type              Load our service plugin   http  is built-in to node   var processor     require    app js                        Load our processor  the code you write    var connection    data createConnection   host  config data host  user  config data user  password  config data pass  database  config data name     var server        service createServer processor   connection connect    server listen config service port  function     console log   s service listening on port  s   config service type  config service port         app js     the code that powers your protocol-agnostic and data-source agnostic service   module exports   function request  response       response end  Responding to      request url       Using this pattern  you can now load community and user config stuff on top of your booted app  dev ops is ready to shove your work into a container and scale it   You re read for multitenant   Userland is isolated   You can now separate the concerns of which service protocol you re using  which database type you re using  and just focus on writing good code   Because you re using layers  you can rely on a single source of truth for everything  at any time  the layered config object   and avoid error checks at every step  worrying about  oh crap  how am I going to make this work without proper config

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JSON parse  your string      That s all

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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          gt  goodResult  continue processing  if    isError badResult        console log  badResult  handle error      else      console log  badResult  continue processing          gt  badResult  handle error

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use the JSON object   JSON parse str

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