Safely turning a JSON string into an object

Question

Given a string of JSON data  how can I safely turn that string into a JavaScript object   Obviously I can do this unsafely with something like   var obj   eval       json           but that leaves me vulnerable to the JSON string containing other code  which it seems very dangerous to simply eval

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Official documentation   The JSON parse   method parses a JSON string  constructing the JavaScript value or object described by the string  An optional reviver function can be provided to perform a transformation on the resulting object before it is returned   Syntax   JSON parse text   reviver     Parameters   text   The string to parse as JSON  See the JSON object for a description of JSON syntax   reviver  optional    If a function  this prescribes how the value originally produced by parsing is transformed  before being returned   Return value  The Object corresponding to the given JSON text   Exceptions  Throws a SyntaxError exception if the string to parse is not valid JSON

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If you re using jQuery  you can also use     getJSON url  function data          Then you can do things like  data key1 something data key1 something else   etc

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I found a  better  way   In CoffeeScript   try data   JSON parse jqxhr responseText  data       message   Server error  please retry      In Javascript   var data   try     data   JSON parse jqxhr responseText     catch   error      data     data       message   Server error  please retry

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JSON parsing is always a pain  If the input is not as expected it throws an error and crashes what you are doing    You can use the following tiny function to safely parse your input  It always turns an object even if the input is not valid or is already an object which is better for most cases   JSON safeParse   function  input  def         Convert null to empty object   if   input        return def            else if  Object prototype toString call input        object Object          return input        try       return JSON parse input       catch  e        return def

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Just for fun  here is a way using a function    jsonObject    new Function  return     jsonFormatData

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This seems to be the issue   An input that is received via Ajax websocket etc  and it will be in String format   but you need to know if it is JSON parsable  The touble is  if you always run it through JSON parse  the program MAY continue  successfully  but you ll still see an error thrown in the console with the dreaded  Error  unexpected token  x     var data   try     data   JSON parse jqxhr responseText     catch   error      data     data       message   Server error  please retry

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Just to the cover parse for different input types  Parse the data with JSON parse    and the data becomes a JavaScript object   var obj   JSON parse     name   John    age  30   city   New York        When using the JSON parse   on a JSON derived from an array  the method will return a JavaScript array  instead of a JavaScript object   var myArr   JSON parse this responseText   console log myArr 0      Date objects are not allowed in JSON  For Dates do somthing like this  var text       name   John    birth   1986-12-14    city   New York     var obj   JSON parse text   obj birth   new Date obj birth     Functions are not allowed in JSON  If you need to include a function  write it as a string   var text       name   John    age   function     return 30      city   New York     var obj   JSON parse text   obj age   eval       obj age

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If we have a string like this       status   1   token     65b4352b2dfc4957a09add0ce5714059       then we can simply use JSON parse twice to convert this string to a JSON object   var sampleString       status   1   token     65b4352b2dfc4957a09add0ce5714059     var jsonString  JSON parse sampleString  var jsonObject  JSON parse jsonString    And we can extract values from the JSON object using      instead of last JSON parse  var   status  token     JSON parse jsonString     The result will be   status   1 and token   65b4352b2dfc4957a09add0ce5714059

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JSON parse jsonString     json parse will change into object

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JSON parse is the right way to convert a string into an object but if the string that is parsed is not object or if the string is not correct then it will throw an error that will cause the rest of the code to break so it is ideal to wrap the JSON parse function inside try-catch like   try     let obj   JSON parse string    catch err      console log err

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You also can use reviver function to filter   var data   JSON parse jsonString  function reviver key  value         your code here to filter       For more information read JSON parse

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Parse the JSON string with JSON parse    and the data becomes a JavaScript object   JSON parse jsonString    Here  JSON represents to process JSON dataset   Imagine we received this text from a web server       name   John    age  30   city   New York      To parse into a JSON object   var obj   JSON parse     name   John    age  30   city   New York         Here obj is the respective JSON object which looks like      name   John    age  30   city   New York     To fetch a value use the   operator   obj name    John obj age   30   Convert a JavaScript object into a string with JSON stringify

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Try using the method with this Data object   ex Data   result true count 1    try     eval  var obj     Data     console log obj count     catch e      console log e message       This method really helps in Nodejs when you are working with serial port programming

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ajax     url  url    dataType   json     data  data    success  callback       The callback is passed the returned data  which will be a JavaScript object or array as defined by the JSON structure and parsed using the   parseJSON   method

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Using JSON parse is probably the best way    Here s an example live demo   var jsonRes       students                       firstName   Michel     lastName   John    age  18                    firstName   Richard     lastName   Joe   age  20                     firstName   James     lastName   Henry   age  15        var studentObject   JSON parse jsonRes

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Try this This one is written in typescript            export function safeJsonParse str  string                   try                    return JSON parse str                        catch  e                     return str

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This answer is for IE  lt  7  for modern browsers check Jonathan s answer above   This answer is outdated and Jonathan s answer above  JSON parse jsonString   is now the best answer   JSON org has JSON parsers for many languages including four different ones for JavaScript   I believe most people would consider json2 js their goto implementation

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JSON parse jsonString  is a pure JavaScript approach so long as you can guarantee a reasonably modern browser

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I m not sure about other ways to do it but here s how you do it in Prototype  JSON tutorial    new Ajax Request   some url       method  get     requestHeaders   Accept   application json      onSuccess  function transport       var json   transport responseText evalJSON true             Calling evalJSON   with true as the argument sanitizes the incoming string

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Use the simple code example in  JSON parse      var jsontext      firstname   Jesper   surname   Aaberg   phone    555-0100   555-0120      var contact   JSON parse jsontext     and reversing it   var str   JSON stringify arr

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JSON parse   converts any JSON string passed into the function into a JSON object   To understand it better  press F12 to open  Inspect Element  in your browser and go to the console to write the following commands   var response      result  true  count  1      sample json object string form  JSON parse response     converts passed string to JSON Object    Now run the command   console log JSON parse response      You ll get output as an Object  result  true  count  1    In order to use that Object  you can assign it to the variable  maybe obj   var obj   JSON parse response     By using obj and the dot     operator you can access properties of the JSON object   Try to run the command   console log obj result

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Safely turning a JSON string into an object        param  String  str - JSON String     returns deserialized object  false if error     export function jsonParse str      let data   null    try       data   JSON parse str       catch  err        return false        return data

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The jQuery method is now deprecated  Use this method instead   let jsonObject   JSON parse jsonString       Original answer using deprecated jQuery functionality   If you re using jQuery just use   jQuery parseJSON  jsonString      It s exactly what you re looking for  see the jQuery documentation

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Summary   Javascript  both browser and NodeJS  have a built in JSON object  On this Object are 2 convenient methods for dealing with JSON  They are the following    JSON parse        Takes JSON as argument  returns JS object JSON stringify    Takes JS object as argument returns JSON object   Other applications   Besides for very conveniently dealing with JSON they have can be used for other means   The combination of both JSON methods allows us to make very easy make deep clones of arrays or objects  For example    x000D   x000D  let arr1    1  2   3  4    x000D  let newArr   arr1 slice    x000D   x000D  arr1 2  0     changed    x000D  console log newArr      not a deep clone x000D   x000D  let arr2    1  2   3  4    x000D  let newArrDeepclone   JSON parse JSON stringify arr2    x000D   x000D  arr2 2  0     changed    x000D  console log newArrDeepclone      A deep clone  values unchanged x000D   x000D   x000D

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The easiest way using parse   method   var response      result  true  count  1    var JsonObject  JSON parse response     Then you can get the values of the JSON elements  for example   var myResponseResult   JsonObject result  var myResponseCount   JsonObject count    Using jQuery as described in the jQuery parseJSON   documentation   JSON parse jsonString

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Older question  I know  however nobody notice this solution by using new Function    an anonymous function that returns the data      Just an example    var oData    test1  This is my object  test2  This is my object      if  typeof oData      object      try      oData    new Function  return    oData                 catch e    oData false      if  typeof oData      object        alert   Error in code        else           alert  oData test1            alert  oData test2                This is a little more safe because it executes inside a function and do not compile in your code directly  So if there is a function declaration inside it  it will not be bound to the default window object    I use this to  compile  configuration settings of DOM elements  for example the data attribute  simple and fast

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Converting the object to JSON  and then parsing it  works for me  like   JSON parse JSON stringify object

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Performance There are already good answer for this question  but I was curious about performance and today 2020 09 21 I conduct tests on MacOs HighSierra 10 13 6 on Chrome v85  Safari v13 1 2 and Firefox v80 for chosen solutions  Results  eval Function  A B C  approach is fast on Chrome  but for big-deep object N 1000 they crash   quot maximum stack call exceed  eval  A  is fast medium fast on all browsers JSON parse  D E  are fastest on Safari and Firefox   Details I perform 4 tests cases   for small shallow object HERE for small deep object HERE for big shallow object HERE for big deep object HERE  Object used in above tests came from HERE  x000D   x000D  let obj ShallowSmall       field0  false    field1  true    field2  1    field3  0    field4  null    field5        field6        field7   text7     field8   text8      let obj DeepSmall       level0       level1        level2         level3          level4           level5            level6             level7              level8               level9             abc                              let obj ShallowBig   Array 1000  fill 0  reduce  a c i    gt   a  field  i  getField i  a          let obj DeepBig   genDeepObject 1000         ------------------    Show objects    ------------------  console log  obj ShallowSmall   JSON stringify obj ShallowSmall    console log  obj DeepSmall   JSON stringify obj DeepSmall    console log  obj ShallowBig   JSON stringify obj ShallowBig    console log  obj DeepBig   JSON stringify obj DeepBig           ------------------    HELPERS    ------------------  function getField k      let i k 10    if i  0  return false    if i  1  return true    if i  2  return k    if i  3  return 0    if i  4  return null    if i  5  return       if i  6  return         if i gt  7  return  text  k     function genDeepObject N         generate   level0  level1     levelN   end       N-times     abc                     let obj       let o obj    let arr         let a arr     for let i 0  i lt N  i          o  level  i          o o  level  i       let aa         a push aa       a aa         a 0   abc     o  end   arr    return obj    x000D   x000D   x000D   Below snippet presents chosen solutions  x000D   x000D     src  https   stackoverflow com q 45015 860099 function A json      return eval       json               https   stackoverflow com a 26377600 860099 function B json      return  new Function  return    json                improved https   stackoverflow com a 26377600 860099 function C json      return Function  return    json              src  https   stackoverflow com a 5686237 860099 function D json      return JSON parse json         src  https   stackoverflow com a 233630 860099 function E json      return   parseJSON json            --------------------    TEST    --------------------  let json      a   abc   b   123   d   1 2 3   e    a  1  b  2  c  3       A B C D E  map f  gt        console log      f name         JSON stringify f json         x000D   lt script src  https   cdnjs cloudflare com ajax libs jquery 3 3 1 jquery min js  gt  lt  script gt  This shippet only presents functions used in performance tests - it not perform tests itself  x000D   x000D   x000D   And here are example results for chrome

[javascript] Safely turning a JSON string into an object

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