How to check if JavaScript object is JSON

Question

I have a nested JSON object that I need to loop through  and the value of each key could be a String  JSON array or another JSON object  Depending on the type of object  I need to carry out different operations  Is there any way I can check the type of the object to see if it is a String  JSON object or JSON array   I tried using typeof and instanceof but both didn t seem to work  as typeof will return an object for both JSON object and array  and instanceof gives an error when I do obj instanceof JSON   To be more specific  after parsing the JSON into a JS object  is there any way I can check if it is a normal string  or an object with keys and values  from a JSON object   or an array  from a JSON array    For example   JSON  var data      hi                  hello                    hi1   hi2                                hey   words                   Sample JavaScript  var jsonObj   JSON parse data   var path     hi   hello     function check jsonObj  path        var parent   jsonObj      for  var i   0  i  lt  path length-1  i              var key   path i           if  parent    undefined                parent   parent key                       if  parent    undefined            var endLength   path length - 1          var child   parent path endLength              if child is a string  add some text           if child is an object  edit the key value           if child is an array  add a new element           if child does not exist  add a new key value           How do I carry out the object checking as shown above

User · Answer

Why not check Number - a bit shorter and works in IE/Chrome/FF/node.js

_x000D_

function whatIsIt(object) {_x000D_
    if (object === null) {_x000D_
        return "null";_x000D_
    }_x000D_
    else if (object === undefined) {_x000D_
        return "undefined";_x000D_
    }_x000D_
    if (object.constructor.name) {_x000D_
            return object.constructor.name;_x000D_
    }_x000D_
    else { // last chance 4 IE: "\nfunction Number() {\n    [native code]\n}\n" / node.js: "function String() { [native code] }"_x000D_
        var name = object.constructor.toString().split(' ');_x000D_
        if (name && name.length > 1) {_x000D_
            name = name[1];_x000D_
            return name.substr(0, name.indexOf('('));_x000D_
        }_x000D_
        else { // unreachable now(?)_x000D_
            return "don't know";_x000D_
        }_x000D_
    }_x000D_
}_x000D_
_x000D_
var testSubjects = ["string", [1,2,3], {foo: "bar"}, 4];_x000D_
// Test all options_x000D_
console.log(whatIsIt(null));_x000D_
console.log(whatIsIt());_x000D_
for (var i=0, len = testSubjects.length; i < len; i++) {_x000D_
    console.log(whatIsIt(testSubjects[i]));_x000D_
}

_x000D_

User · Answer

you can also try to parse the data and then check if you got object   var testIfJson   JSON parse data   if  typeOf testIfJson     object       Json   else     Not Json

User · Answer

I combine the typeof operator with a check of the constructor attribute  by Peter    var typeOf   function object        var firstShot   typeof object      if  firstShot      object             return firstShot             else if  object constructor        constructor            return  array             else if  object constructor        constructor            return  object             else if  object     null            return  null             else           return  don  t know                Test var testSubjects    true  false  1  2 3   string    4 5 6    foo   bar    null  undefined    console log   typeOf      input parameter   join   t    console log new Array 28  join  -     testSubjects map function testSubject       console log  typeOf testSubject   JSON stringify testSubject   join   t t           Result   typeOf      input parameter --------------------------- boolean     true boolean     false number      1 number      2 3 string       string  array        4 5 6  object        foo   bar   null        null undefined

User · Answer

I d check the constructor attribute   e g   var stringConstructor    test  constructor  var arrayConstructor      constructor  var objectConstructor        constructor   function whatIsIt object        if  object     null            return  null             if  object     undefined            return  undefined             if  object constructor     stringConstructor            return  String             if  object constructor     arrayConstructor            return  Array             if  object constructor     objectConstructor            return  Object                       return  don t know            var testSubjects     string    1 2 3    foo   bar    4    for  var i 0  len   testSubjects length  i  lt  len  i          alert whatIsIt testSubjects i         Edit  Added a null check and an undefined check

User · Answer

The answer by  PeterWilkinson didn t work for me because a constructor for a  typed  object is customized to the name of that object  I had to work with typeof  function isJson obj        var t   typeof obj      return   boolean    number    string    symbol    function   indexOf t     -1

User · Answer

I wrote an npm module to solve this problem  It s available here   object-types  a module for finding what literal types underly objects  Install    npm install --save object-types     Usage  const objectTypes   require  object-types     objectTypes          gt   object   objectTypes          gt   array   objectTypes new Object true        gt   boolean    Take a look  it should solve your exact problem  Let me know if you have any questions  https   github com dawsonbotsford object-types

User · Answer

I know this is a very old question with good answers  However  it seems that it s still possible to add my 2   to it   Assuming that you re trying to test not a JSON object itself but a String that is formatted as a JSON  which seems to be the case in your var data   you could use the following function that returns a boolean  is or is not a  JSON     function isJsonString  jsonString           This function below   printError   can be used to print details about the error  if any       Please  refer to the original article  see the end of this post       for more details  I suppressed details to keep the code clean         let printError   function error  explicit      console log     explicit    EXPLICIT     INEXPLICIT      error name     error message             try         JSON parse  jsonString          return true     It s a valid JSON format     catch  e          return false     It s not a valid JSON format          Here are some examples of using the function above   console log   n1 -----------------    let j    abc   console log  j  isJsonString j      console log   n2 -----------------    j      abc    def     console log  j  isJsonString j      console log   n3 -----------------    j      abc    def    console log  j  isJsonString j      console log   n4 -----------------    j         console log  j  isJsonString j      console log   n5 -----------------    j           console log  j  isJsonString j      console log   n6 -----------------    j            console log  j  isJsonString j      console log   n7 -----------------    j       a  1   b     2     c  3     console log  j  isJsonString j       When you run the code above  you will get the following results   1 ----------------- abc false  2 -----------------   abc    def   true  3 -----------------   abc    def  false  4 -----------------    true  5 -----------------      true  6 -----------------       false  7 -----------------    a  1   b     2     c  3   true   Please  try the snippet below and let us know if this works for you      IMPORTANT  the function presented in this post was adapted from https   airbrake io blog javascript-error-handling syntaxerror-json-parse-bad-parsing where you can find more and interesting details about the JSON parse   function    x000D   x000D  function isJsonString  jsonString     x000D   x000D    let printError   function error  explicit    x000D    console log     explicit    EXPLICIT     INEXPLICIT      error name     error message     x000D      x000D   x000D   x000D    try   x000D        JSON parse  jsonString    x000D        return true     It s a valid JSON format x000D      catch  e    x000D        return false     It s not a valid JSON format x000D      x000D   x000D    x000D   x000D   x000D  console log   n1 -----------------    x000D  let j    abc   x000D  console log  j  isJsonString j     x000D   x000D  console log   n2 -----------------    x000D  j      abc    def     x000D  console log  j  isJsonString j     x000D   x000D  console log   n3 -----------------    x000D  j      abc    def    x000D  console log  j  isJsonString j     x000D   x000D  console log   n4 -----------------    x000D  j         x000D  console log  j  isJsonString j     x000D   x000D  console log   n5 -----------------    x000D  j           x000D  console log  j  isJsonString j     x000D   x000D  console log   n6 -----------------    x000D  j            x000D  console log  j  isJsonString j     x000D   x000D  console log   n7 -----------------    x000D  j       a  1   b     2     c  3     x000D  console log  j  isJsonString j     x000D   x000D   x000D

User · Answer

Peter s answer with an additional check  Of course  not 100  guaranteed   var isJson   false  outPutValue      var objectConstructor      constructor  if jsonToCheck constructor     objectConstructor       outPutValue   JSON stringify jsonToCheck       try              JSON parse outPutValue               isJson   true       catch err               isJson   false           if isJson       alert  Is json      JSON stringify jsonToCheck           else      alert  Is other

User · Answer

If you are trying to check the type of an object after you parse a JSON string  I suggest checking the constructor attribute   obj constructor    Array    obj constructor    String    obj constructor    Object   This will be a much faster check than typeof or instanceof   If a JSON library does not return objects constructed with these functions  I would be very suspiciouse of it

User · Answer

try this dirty way          obj  includes

User · Answer

You can use Array isArray to check for arrays   Then typeof obj     string   and typeof obj     object    var s    a string   a       o       i   5  function getType p        if  Array isArray p   return  array       else if  typeof p     string   return  string       else if  p    null  amp  amp  typeof p     object   return  object       else return  other     console log   s  is     getType s    console log   a  is     getType a    console log   o  is     getType o    console log   i  is     getType i          s  is string a  is array  o  is object i  is other

User · Answer

Try this  if   typeof is json     function    function is json   obj         var  has keys   0       for  var  pr in  obj                 if    obj hasOwnProperty   pr    amp  amp        d    test   pr                             has keys   1              break                        return    has keys  amp  amp   obj constructor    Object  amp  amp   obj constructor    Array     1   0       It works for the example below  var  a      name     me           surname     I           nickname                             first     wow                          second     super                          morelevel                                             3level1    1                                         3level2    2                                         3level3    3                                                                       var  b      name    surname    nickname      var  c    abcdefg     console log  is json   a      console log  is json   b      console log  is json   c

User · Answer

You could make your own constructor for JSON parsing   var JSONObj   function obj      extend this  JSON parse obj      var test   new JSONObj    a    apple         a   apple     Then check instanceof to see if it needed parsing originally  test instanceof JSONObj

User · Answer

Based on  Martin Wantke answer  but with some recommended improvements adjusts       NOTE  Check JavaScript type  By Questor function getJSType valToChk         function isUndefined valToChk    return valToChk     undefined        function isNull valToChk    return valToChk     null        function isArray valToChk    return valToChk constructor    Array        function isBoolean valToChk    return valToChk constructor    Boolean        function isFunction valToChk    return valToChk constructor    Function        function isNumber valToChk    return valToChk constructor    Number        function isString valToChk    return valToChk constructor    String        function isObject valToChk    return valToChk constructor    Object         if isUndefined valToChk     return  quot undefined quot         if isNull valToChk     return  quot null quot         if isArray valToChk     return  quot array quot         if isBoolean valToChk     return  quot boolean quot         if isFunction valToChk     return  quot function quot         if isNumber valToChk     return  quot number quot         if isString valToChk     return  quot string quot         if isObject valToChk     return  quot object quot         NOTE  I found this approach very didactic  so I submitted this answer

User · Answer

An JSON object is an object  To check whether a type is an object type  evaluate the constructor property   function isObject obj        return obj     undefined  amp  amp  obj     null  amp  amp  obj constructor    Object      The same applies to all other types   function isArray obj        return obj     undefined  amp  amp  obj     null  amp  amp  obj constructor    Array     function isBoolean obj        return obj     undefined  amp  amp  obj     null  amp  amp  obj constructor    Boolean     function isFunction obj        return obj     undefined  amp  amp  obj     null  amp  amp  obj constructor    Function     function isNumber obj        return obj     undefined  amp  amp  obj     null  amp  amp  obj constructor    Number     function isString obj        return obj     undefined  amp  amp  obj     null  amp  amp  obj constructor    String     function isInstanced obj        if obj     undefined    obj     null    return false         if isArray obj     return false        if isBoolean obj     return false        if isFunction obj     return false        if isNumber obj     return false        if isObject obj     return false        if isString obj     return false         return true

[javascript] How to check if JavaScript object is JSON

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