jQuery won t parse my JSON from AJAX query

Question

I m having difficulty parsing some JSON data returned from my server using jQuery ajax    To perform the AJAX I m using     ajax     url  myUrl    cache  false    dataType   json     success  function data                  error  function e  xhr                       And if I return an array of items then it works fine       title   One   key   1       title   Two   key   2        The success function is called and receives the correct object   However  when I m trying to return a single object     title   One   key   1       The error function is called and xhr contains  parsererror    I ve tried wrapping the JSON in parenthesis on the server before sending it down the wire  but it makes no difference   Yet if I paste the content into a string in Javascript and then use the eval   function  it evaluates it perfectly   Any ideas what I m doing wrong   Anthony

User · Answer

If returning an array works and returning a single object doesn't, you might also try returning your single object as an array containing that single object:

[ { title: "One", key: "1" } ]

that way you are returning a consistent data structure, an array of objects, no matter the data payload.

i see that you've tried wrapping your single object in "parenthesis", and suggest this with example because of course JavaScript treats [ .. ] differently than ( .. )

User · Answer

If jQuery s error handler is being called and the XHR object contains  parser error   that s probably a parser error coming back from the server   Is your multiple result scenario when you call the service without a parameter  but it s breaking when you try to supply a parameter to retrieve the single record    What backend are you returning this from    On ASMX services  for example  that s often the case when parameters are supplied to jQuery as a JSON object instead of a JSON string   If you provide jQuery an actual JSON object for its  data  parameter  it will serialize that into standard  amp  delimited k v pairs instead of sending it as JSON

User · Answer

I had a similar problem to this where Firefox 3 5 worked fine and parsed my JSON data but Firefox 3 0 6 returned a parseerror  Turned out it was a blank space at the start of the JSON that caused Firefox 3 0 6 to throw an error  Removing the blank space fixed it

User · Answer

According to the json org specification  your return is invalid   The names are always quoted  so you should be returning     title    One    key    1      and        title    One    key    1        title    Two    key    2        This may not be the problem with your setup  since you say one of them works now  but it should be fixed for correctness in case you need to switch to another JSON parser in the future

User · Answer

I was getting status   parseerror and xhr status   200   The issue for me was the URL s inside the JSON response had     switching to     fixed this

User · Answer

If you are consuming ASP NET Web Services using jQuery  make sure you have the following included in your web config    lt webServices gt       lt protocols gt           lt add name  HttpGet   gt           lt add name  HttpPost   gt       lt  protocols gt   lt  webServices gt

User · Answer

This problem is usually because your request received the wrong mime type  When developing on your own computer  sometimes you are not receiving the proper mime type from the  server   which is your own computer  I ran into this problem once when developing by opening the locally stored file in the browser  e g  the url was  c  project test html     Try using the beforeSend property to add a  callback function that overrides the mime type  This will trick the code into dealing with json despite the wrong mime type being sent by the server and received by your calling code  Some example code is below   The proper mime type is application json according to this question  but I do know that application j-son worked when I tried it  now several years ago   You should probably try application json first   var jsonMimeType    application json charset UTF-8     ajax    type   GET    url  myURL   beforeSend  function x      if x  amp  amp  x overrideMimeType       x overrideMimeType jsonMimeType            dataType   json    success  function data        do stuff

User · Answer

If you are echoing out the json response and your headers don t match   json then you can use the built in jQuery parseJSON api to parse the response   response      name   John     var obj   jQuery parseJSON response   alert  obj name      John

User · Answer

use   data   yourarray     json encode  data    on server side  On client side use ajax with Datatype JSON and be sure your document encoding is not UTF-8 with BOM it has to be UTF-8

User · Answer

If you are consuming ASP NET Web Services using jQuery  make sure you have the following included in your web config    lt webServices gt       lt protocols gt           lt add name  HttpGet   gt           lt add name  HttpPost   gt       lt  protocols gt   lt  webServices gt

User · Answer

I found in some of my implementations I had to add   obj   new Object  obj    data obj     which seemed to solve the problem  Eval or not it seemed to do exactly the same for me

User · Answer

If jQuery s error handler is being called and the XHR object contains  parser error   that s probably a parser error coming back from the server   Is your multiple result scenario when you call the service without a parameter  but it s breaking when you try to supply a parameter to retrieve the single record    What backend are you returning this from    On ASMX services  for example  that s often the case when parameters are supplied to jQuery as a JSON object instead of a JSON string   If you provide jQuery an actual JSON object for its  data  parameter  it will serialize that into standard  amp  delimited k v pairs instead of sending it as JSON

User · Answer

According to the json org specification  your return is invalid   The names are always quoted  so you should be returning     title    One    key    1      and        title    One    key    1        title    Two    key    2        This may not be the problem with your setup  since you say one of them works now  but it should be fixed for correctness in case you need to switch to another JSON parser in the future

User · Answer

JSON strings are wrapped in double quotes  single quotes are not a valid substitute     who    Hello World     is valid but this is not       who    Hello World     Whilst not the OP s issue  thought it worth noting for others who land here

User · Answer

title   One   key   1      Is not what you think  As an expression  it s an Object literal  but as a statement  it s                       new block     title           define a label called  title  for goto statements          One        statement  the start of an expression which will be ignored         key            er  what  you can t have a goto label in the middle of an expression                     ERROR   Unfortunately eval   does not give you a way to specify whether you are giving it a statement or an expression  and it tends to guess wrong   The usual solution is indeed to wrap anything in parentheses before sending it to the eval   function  You say you ve tried that on the server    clearly somehow that isn t getting through  It should be waterproof to say on the client end  whatever is receiving the XMLHttpRequest response   eval     responseText         instead of   eval responseText     as long as the response is really an expression not a statement   eg  it doesn t have multiple  semicolon-or-newline-separated clauses

User · Answer

In a ColdFusion environment  one thing that will cause an error  even with well-formed JSON  is having Enable Request Debugging Output turned on in the ColdFusion Administrator  under Debugging  amp  Logging   Debug Output Settings   Debugging information will be returned with the JSON data and will thus make it invalid

User · Answer

If returning an array works and returning a single object doesn't, you might also try returning your single object as an array containing that single object:

[ { title: "One", key: "1" } ]

that way you are returning a consistent data structure, an array of objects, no matter the data payload.

i see that you've tried wrapping your single object in "parenthesis", and suggest this with example because of course JavaScript treats [ .. ] differently than ( .. )

User · Answer

This problem is usually because your request received the wrong mime type  When developing on your own computer  sometimes you are not receiving the proper mime type from the  server   which is your own computer  I ran into this problem once when developing by opening the locally stored file in the browser  e g  the url was  c  project test html     Try using the beforeSend property to add a  callback function that overrides the mime type  This will trick the code into dealing with json despite the wrong mime type being sent by the server and received by your calling code  Some example code is below   The proper mime type is application json according to this question  but I do know that application j-son worked when I tried it  now several years ago   You should probably try application json first   var jsonMimeType    application json charset UTF-8     ajax    type   GET    url  myURL   beforeSend  function x      if x  amp  amp  x overrideMimeType       x overrideMimeType jsonMimeType            dataType   json    success  function data        do stuff

User · Answer

The techniques  eval    and  JSON parse    use mutually exclusive formats      With  eval    parenthesis are required  With  JSON parse    parenthesis are forbidden    Beware  there are  stringify    functions that produce  eval  format   For ajax  you should use only the JSON format     While  eval  incorporates the entire JavaScript language  JSON uses only a tiny subset of the language   Among the constructs in the JavaScript language that  eval  must recognize is the  Block statement   a k a   compound statement    which is a pair or curly braces      with some statements inside   But curly braces are also used in the syntax of object literals   The interpretation is differentiated by the context in which the code appears   Something might look like an object literal to you  but  eval  will see it as a compound statement     In the JavaScript language  object literals occur to the right of an assignment   var myObj        some  code  here         Object literals don t occur on their own        some  code  here           this looks like a compound statement   Going back to the OP s original question  asked in 2008  he inquired why the following fails in  eval        title   One   key   1      The answer is that it looks like a compound statement   To convert it into an object  you must put it into a context where a compound statement is impossible   That is done by putting parenthesis around it      title   One   key   1            not a compound statment  so must be object literal   The OP also asked why a similar statement did successfully eval       title   One   key   1       title   Two   key   2        The same answer applies -- the curly braces are in a context where a compound statement is impossible   This is an array context           and arrays can contain objects  but they cannot contain statements   Unlike  eval     JSON is very limited in its capabilities   The limitation is intentional   The designer of JSON intended a minimalist subset of JavaScript  using only syntax that could appear on the right hand side of an assignment   So if you have some code that correctly parses in JSON     var myVar   JSON parse     some   code   here            that implies it will also legally parse on the right hand side of an assignment  like this    var myVar      some  code  here        But that is not the only restriction on JSON   The BNF language specification for JSON is very simple  For example  it does not allow for the use of single quotes to indicate strings  like JavaScript and Perl do  and it does not have a way to express a single character as a byte  like  C  does    Unfortunately  it also does not allow comments  which would be really nice when creating configuration files    The upside of all those limitations is that parsing JSON is fast and offers no opportunity for code injection  a security threat      Because of these limitations  JSON has no use for parenthesis   Consequently  a parenthesis in a JSON string is an illegal character   Always use JSON format with ajax  for the following reasons    A typical ajax pipeline will be configured for JSON  The use of  eval    will be criticised as a security risk    As an example of an ajax pipeline  consider a program that involves a Node server and a jQuery client   The client program uses a jQuery call having the form   ajax  dataType  json     etc       JQuery creates a jqXHR object for later use  then packages and sends the associated request   The server accepts the request  processes it  and then is ready to respond   The server program will call the method res json data  to package and send the response   Back at the client side  jQuery accepts the response  consults the associated jqXHR object  and processes the JSON formatted data   This all works without any need for manual data conversion  The response involves no explicit call to JSON stringify   on the Node server  and no explicit call to JSON parse   on the client  that s all handled for you   The use of  eval  is associated with code injection security risks  You might think there is no way that can happen  but hackers can get quite creative   Also   eval  is problematic for Javascript optimization   If you do find yourself using a using a  stringify    function  be aware that some functions with that name will create strings that are compatible with  eval  and not with JSON   For example  in Node  the following gives you function that creates strings in  eval  compatible format   var stringify   require  node-stringify       generates eval   format   This can be useful  but unless you have a specific need  it s probably not what you want

User · Answer

jQuery chokes on certain JSON keys  I was sending this JSON snippet in PHP   echo json encode  object  array  result    gt   success       Renaming the  result  key to something else works  I would guess this is a reserved word collision of some kind  and could be a bug in jQuery  1 4 2

User · Answer

If returning an array works and returning a single object doesn't, you might also try returning your single object as an array containing that single object:

[ { title: "One", key: "1" } ]

that way you are returning a consistent data structure, an array of objects, no matter the data payload.

i see that you've tried wrapping your single object in "parenthesis", and suggest this with example because of course JavaScript treats [ .. ] differently than ( .. )

User · Answer

If jQuery s error handler is being called and the XHR object contains  parser error   that s probably a parser error coming back from the server   Is your multiple result scenario when you call the service without a parameter  but it s breaking when you try to supply a parameter to retrieve the single record    What backend are you returning this from    On ASMX services  for example  that s often the case when parameters are supplied to jQuery as a JSON object instead of a JSON string   If you provide jQuery an actual JSON object for its  data  parameter  it will serialize that into standard  amp  delimited k v pairs instead of sending it as JSON

User · Answer

This problem is usually because your request received the wrong mime type  When developing on your own computer  sometimes you are not receiving the proper mime type from the  server   which is your own computer  I ran into this problem once when developing by opening the locally stored file in the browser  e g  the url was  c  project test html     Try using the beforeSend property to add a  callback function that overrides the mime type  This will trick the code into dealing with json despite the wrong mime type being sent by the server and received by your calling code  Some example code is below   The proper mime type is application json according to this question  but I do know that application j-son worked when I tried it  now several years ago   You should probably try application json first   var jsonMimeType    application json charset UTF-8     ajax    type   GET    url  myURL   beforeSend  function x      if x  amp  amp  x overrideMimeType       x overrideMimeType jsonMimeType            dataType   json    success  function data        do stuff

User · Answer

According to the json org specification  your return is invalid   The names are always quoted  so you should be returning     title    One    key    1      and        title    One    key    1        title    Two    key    2        This may not be the problem with your setup  since you say one of them works now  but it should be fixed for correctness in case you need to switch to another JSON parser in the future

User · Answer

I found in some of my implementations I had to add   obj   new Object  obj    data obj     which seemed to solve the problem  Eval or not it seemed to do exactly the same for me

User · Answer

You will to have to set header content type in your php like this     lt  php   header  Content-type application json        gt    Watch these Video for better understanding       Reference  http   www youtube com watch v EvFXWqEqh6o

User · Answer

I had this issue and for a bit I used   eval     data        to get the data returned in an object   but then later had other issues getting a  missing   in parenthetical  error and found out that jQuery has a function specifically for evaluating a string for a json structure       parseJSON data    should do the trick   This is in addition to having your json string in the proper format of course

User · Answer

You will to have to set header content type in your php like this     lt  php   header  Content-type application json        gt    Watch these Video for better understanding       Reference  http   www youtube com watch v EvFXWqEqh6o

User · Answer

If you are echoing out the json response and your headers don t match   json then you can use the built in jQuery parseJSON api to parse the response   response      name   John     var obj   jQuery parseJSON response   alert  obj name      John

User · Answer

I found in some of my implementations I had to add   obj   new Object  obj    data obj     which seemed to solve the problem  Eval or not it seemed to do exactly the same for me

User · Answer

If returning an array works and returning a single object doesn't, you might also try returning your single object as an array containing that single object:

[ { title: "One", key: "1" } ]

that way you are returning a consistent data structure, an array of objects, no matter the data payload.

i see that you've tried wrapping your single object in "parenthesis", and suggest this with example because of course JavaScript treats [ .. ] differently than ( .. )

User · Answer

If jQuery s error handler is being called and the XHR object contains  parser error   that s probably a parser error coming back from the server   Is your multiple result scenario when you call the service without a parameter  but it s breaking when you try to supply a parameter to retrieve the single record    What backend are you returning this from    On ASMX services  for example  that s often the case when parameters are supplied to jQuery as a JSON object instead of a JSON string   If you provide jQuery an actual JSON object for its  data  parameter  it will serialize that into standard  amp  delimited k v pairs instead of sending it as JSON

User · Answer

I was struggling with this  and spent a few hours trying to figure this out  until I used firebug to show the data object   var data   eval       data responseText         console log data count

User · Answer

Is your server sending data as Content-Type    json   If not  modify the response headers accordingly  Sending  application json  would be fine  for example

User · Answer

JSON strings are wrapped in double quotes  single quotes are not a valid substitute     who    Hello World     is valid but this is not       who    Hello World     Whilst not the OP s issue  thought it worth noting for others who land here

User · Answer

This problem is usually because your request received the wrong mime type  When developing on your own computer  sometimes you are not receiving the proper mime type from the  server   which is your own computer  I ran into this problem once when developing by opening the locally stored file in the browser  e g  the url was  c  project test html     Try using the beforeSend property to add a  callback function that overrides the mime type  This will trick the code into dealing with json despite the wrong mime type being sent by the server and received by your calling code  Some example code is below   The proper mime type is application json according to this question  but I do know that application j-son worked when I tried it  now several years ago   You should probably try application json first   var jsonMimeType    application json charset UTF-8     ajax    type   GET    url  myURL   beforeSend  function x      if x  amp  amp  x overrideMimeType       x overrideMimeType jsonMimeType            dataType   json    success  function data        do stuff

User · Answer

If you are consuming ASP NET Web Services using jQuery  make sure you have the following included in your web config    lt webServices gt       lt protocols gt           lt add name  HttpGet   gt           lt add name  HttpPost   gt       lt  protocols gt   lt  webServices gt

User · Answer

also try this    ajax       url  url      data datas      success function datas  textStatus  jqXHR       var returnedData   jQuery parseJSON datas substr datas indexOf                in my case server responds with unknow character before

User · Answer

use   data   yourarray     json encode  data    on server side  On client side use ajax with Datatype JSON and be sure your document encoding is not UTF-8 with BOM it has to be UTF-8

User · Answer

Is your server sending data as Content-Type    json   If not  modify the response headers accordingly  Sending  application json  would be fine  for example

User · Answer

Is your server sending data as Content-Type    json   If not  modify the response headers accordingly  Sending  application json  would be fine  for example

User · Answer

I found in some of my implementations I had to add   obj   new Object  obj    data obj     which seemed to solve the problem  Eval or not it seemed to do exactly the same for me

User · Answer

title   One   key   1      Is not what you think  As an expression  it s an Object literal  but as a statement  it s                       new block     title           define a label called  title  for goto statements          One        statement  the start of an expression which will be ignored         key            er  what  you can t have a goto label in the middle of an expression                     ERROR   Unfortunately eval   does not give you a way to specify whether you are giving it a statement or an expression  and it tends to guess wrong   The usual solution is indeed to wrap anything in parentheses before sending it to the eval   function  You say you ve tried that on the server    clearly somehow that isn t getting through  It should be waterproof to say on the client end  whatever is receiving the XMLHttpRequest response   eval     responseText         instead of   eval responseText     as long as the response is really an expression not a statement   eg  it doesn t have multiple  semicolon-or-newline-separated clauses

User · Answer

The techniques  eval    and  JSON parse    use mutually exclusive formats      With  eval    parenthesis are required  With  JSON parse    parenthesis are forbidden    Beware  there are  stringify    functions that produce  eval  format   For ajax  you should use only the JSON format     While  eval  incorporates the entire JavaScript language  JSON uses only a tiny subset of the language   Among the constructs in the JavaScript language that  eval  must recognize is the  Block statement   a k a   compound statement    which is a pair or curly braces      with some statements inside   But curly braces are also used in the syntax of object literals   The interpretation is differentiated by the context in which the code appears   Something might look like an object literal to you  but  eval  will see it as a compound statement     In the JavaScript language  object literals occur to the right of an assignment   var myObj        some  code  here         Object literals don t occur on their own        some  code  here           this looks like a compound statement   Going back to the OP s original question  asked in 2008  he inquired why the following fails in  eval        title   One   key   1      The answer is that it looks like a compound statement   To convert it into an object  you must put it into a context where a compound statement is impossible   That is done by putting parenthesis around it      title   One   key   1            not a compound statment  so must be object literal   The OP also asked why a similar statement did successfully eval       title   One   key   1       title   Two   key   2        The same answer applies -- the curly braces are in a context where a compound statement is impossible   This is an array context           and arrays can contain objects  but they cannot contain statements   Unlike  eval     JSON is very limited in its capabilities   The limitation is intentional   The designer of JSON intended a minimalist subset of JavaScript  using only syntax that could appear on the right hand side of an assignment   So if you have some code that correctly parses in JSON     var myVar   JSON parse     some   code   here            that implies it will also legally parse on the right hand side of an assignment  like this    var myVar      some  code  here        But that is not the only restriction on JSON   The BNF language specification for JSON is very simple  For example  it does not allow for the use of single quotes to indicate strings  like JavaScript and Perl do  and it does not have a way to express a single character as a byte  like  C  does    Unfortunately  it also does not allow comments  which would be really nice when creating configuration files    The upside of all those limitations is that parsing JSON is fast and offers no opportunity for code injection  a security threat      Because of these limitations  JSON has no use for parenthesis   Consequently  a parenthesis in a JSON string is an illegal character   Always use JSON format with ajax  for the following reasons    A typical ajax pipeline will be configured for JSON  The use of  eval    will be criticised as a security risk    As an example of an ajax pipeline  consider a program that involves a Node server and a jQuery client   The client program uses a jQuery call having the form   ajax  dataType  json     etc       JQuery creates a jqXHR object for later use  then packages and sends the associated request   The server accepts the request  processes it  and then is ready to respond   The server program will call the method res json data  to package and send the response   Back at the client side  jQuery accepts the response  consults the associated jqXHR object  and processes the JSON formatted data   This all works without any need for manual data conversion  The response involves no explicit call to JSON stringify   on the Node server  and no explicit call to JSON parse   on the client  that s all handled for you   The use of  eval  is associated with code injection security risks  You might think there is no way that can happen  but hackers can get quite creative   Also   eval  is problematic for Javascript optimization   If you do find yourself using a using a  stringify    function  be aware that some functions with that name will create strings that are compatible with  eval  and not with JSON   For example  in Node  the following gives you function that creates strings in  eval  compatible format   var stringify   require  node-stringify       generates eval   format   This can be useful  but unless you have a specific need  it s probably not what you want

User · Answer

jQuery chokes on certain JSON keys  I was sending this JSON snippet in PHP   echo json encode  object  array  result    gt   success       Renaming the  result  key to something else works  I would guess this is a reserved word collision of some kind  and could be a bug in jQuery  1 4 2

User · Answer

I was struggling with this  and spent a few hours trying to figure this out  until I used firebug to show the data object   var data   eval       data responseText         console log data count

User · Answer

I was getting status   parseerror and xhr status   200   The issue for me was the URL s inside the JSON response had     switching to     fixed this

User · Answer

I had a similar problem to this where Firefox 3 5 worked fine and parsed my JSON data but Firefox 3 0 6 returned a parseerror  Turned out it was a blank space at the start of the JSON that caused Firefox 3 0 6 to throw an error  Removing the blank space fixed it

User · Answer

also try this    ajax       url  url      data datas      success function datas  textStatus  jqXHR       var returnedData   jQuery parseJSON datas substr datas indexOf                in my case server responds with unknow character before

User · Answer

title   One   key   1      Is not what you think  As an expression  it s an Object literal  but as a statement  it s                       new block     title           define a label called  title  for goto statements          One        statement  the start of an expression which will be ignored         key            er  what  you can t have a goto label in the middle of an expression                     ERROR   Unfortunately eval   does not give you a way to specify whether you are giving it a statement or an expression  and it tends to guess wrong   The usual solution is indeed to wrap anything in parentheses before sending it to the eval   function  You say you ve tried that on the server    clearly somehow that isn t getting through  It should be waterproof to say on the client end  whatever is receiving the XMLHttpRequest response   eval     responseText         instead of   eval responseText     as long as the response is really an expression not a statement   eg  it doesn t have multiple  semicolon-or-newline-separated clauses

User · Answer

title   One   key   1      Is not what you think  As an expression  it s an Object literal  but as a statement  it s                       new block     title           define a label called  title  for goto statements          One        statement  the start of an expression which will be ignored         key            er  what  you can t have a goto label in the middle of an expression                     ERROR   Unfortunately eval   does not give you a way to specify whether you are giving it a statement or an expression  and it tends to guess wrong   The usual solution is indeed to wrap anything in parentheses before sending it to the eval   function  You say you ve tried that on the server    clearly somehow that isn t getting through  It should be waterproof to say on the client end  whatever is receiving the XMLHttpRequest response   eval     responseText         instead of   eval responseText     as long as the response is really an expression not a statement   eg  it doesn t have multiple  semicolon-or-newline-separated clauses

User · Answer

If you are consuming ASP NET Web Services using jQuery  make sure you have the following included in your web config    lt webServices gt       lt protocols gt           lt add name  HttpGet   gt           lt add name  HttpPost   gt       lt  protocols gt   lt  webServices gt

User · Answer

I had this issue and for a bit I used   eval     data        to get the data returned in an object   but then later had other issues getting a  missing   in parenthetical  error and found out that jQuery has a function specifically for evaluating a string for a json structure       parseJSON data    should do the trick   This is in addition to having your json string in the proper format of course

User · Answer

Is your server sending data as Content-Type    json   If not  modify the response headers accordingly  Sending  application json  would be fine  for example

User · Answer

According to the json org specification  your return is invalid   The names are always quoted  so you should be returning     title    One    key    1      and        title    One    key    1        title    Two    key    2        This may not be the problem with your setup  since you say one of them works now  but it should be fixed for correctness in case you need to switch to another JSON parser in the future

User · Answer

In a ColdFusion environment  one thing that will cause an error  even with well-formed JSON  is having Enable Request Debugging Output turned on in the ColdFusion Administrator  under Debugging  amp  Logging   Debug Output Settings   Debugging information will be returned with the JSON data and will thus make it invalid

[jquery] jQuery won't parse my JSON from AJAX query

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