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Uncaught SyntaxError: Unexpected token with JSON.parse

Posted by: admin November 29, 2017 Leave a comment

Questions:

what causes this error on the third line?

var products = [{
  "name": "Pizza",
  "price": "10",
  "quantity": "7"
}, {
  "name": "Cerveja",
  "price": "12",
  "quantity": "5"
}, {
  "name": "Hamburguer",
  "price": "10",
  "quantity": "2"
}, {
  "name": "Fraldas",
  "price": "6",
  "quantity": "2"
}];
console.log(products);
var b = JSON.parse(products); //unexpected token o
Answers:

products is an object. (creating from an object literal)

JSON.parse() is used to convert a string containing JSON notation into a Javascript object.

Your code turns the object into a string (by calling .toString()) in order to try to parse it as JSON text.
The default .toString() returns "[object Object]", which is not valid JSON; hence the error.

Questions:
Answers:

Let’s say you know it’s valid JSON but your are still getting this…

In that case it’s likely that there are hidden/special characters in the string from whatever source your getting them. When you paste into a validator, they are lost – but in the string they are still there. Those chars, while invisible, will break JSON.parse()

If s is your raw JSON, then clean it up with:

// preserve newlines, etc - use valid JSON
s = s.replace(/\n/g, "\n")  
               .replace(/\'/g, "\'")
               .replace(/\"/g, '\"')
               .replace(/\&/g, "\&")
               .replace(/\r/g, "\r")
               .replace(/\t/g, "\t")
               .replace(/\b/g, "\b")
               .replace(/\f/g, "\f");
// remove non-printable and other non-valid JSON chars
s = s.replace(/[\u0000-\u0019]+/g,""); 
var o = JSON.parse(s);

Questions:
Answers:

It seems you want to stringify the object.
So, you should use:

JSON.stringify(products);

The reason for the error is that JSON.parse() expects a String value and products is an Array.

Note: I think it attempts json.parse('[object Array]') which complains it didn’t expect token o after [.

Questions:
Answers:

I found the same issue with JSON.parse(inputString).

In my case the input string is coming from my server page [return of a page method].

I printed the typeof(inputString) – it was string, still the error occurs.

I also tried JSON.stringify(inputString), but it did not help.

Later I found this to be an issue with the new line operator [\n], inside a field value.

I did a replace [with some other character, put the new line back after parse] and everything is working fine.

Questions:
Answers:
products = [{"name":"Pizza","price":"10","quantity":"7"}, {"name":"Cerveja","price":"12","quantity":"5"}, {"name":"Hamburguer","price":"10","quantity":"2"}, {"name":"Fraldas","price":"6","quantity":"2"}];

change to

products = '[{"name":"Pizza","price":"10","quantity":"7"}, {"name":"Cerveja","price":"12","quantity":"5"}, {"name":"Hamburguer","price":"10","quantity":"2"}, {"name":"Fraldas","price":"6","quantity":"2"}]';

Questions:
Answers:

JSON.parse is waiting for a String in parameter. You need to stringify your JSON object to solve the problem.

products = [{"name":"Pizza","price":"10","quantity":"7"}, {"name":"Cerveja","price":"12","quantity":"5"}, {"name":"Hamburguer","price":"10","quantity":"2"}, {"name":"Fraldas","price":"6","quantity":"2"}];
console.log(products);
var b = JSON.parse(JSON.stringify(products));  //solves the problem

Questions:
Answers:
[
  {
    "name": "Pizza",
    "price": "10",
    "quantity": "7"
  },
  {
    "name": "Cerveja",
    "price": "12",
    "quantity": "5"
  },
  {
    "name": "Hamburguer",
    "price": "10",
    "quantity": "2"
  },
  {
    "name": "Fraldas",
    "price": "6",
    "quantity": "2"
  }
]

Here is your perfect Json that you can parse.

Questions:
Answers:

When you are using POST or PUT method, make sure to stringify the body part.

I have documented an example here
https://gist.github.com/manju16832003/4a92a2be693a8fda7ca84b58b8fa7154

Questions:
Answers:

One other gotcha that can result in "SyntaxError: Unexpected token" exception when calling JSON.parse() is using any of the following in the string values:

  1. New-line characters.

  2. Tabs (yes, tabs that you can produce with the Tab key!)

  3. Any stand-alone slash \ (but for some reason not /, at least not on Chrome.)

(For a full list see the String section here.)

For instance the following will get you this exception:

{
    "msg" : {
        "message": "It cannot
contain a new-line",
        "description": "Some discription with a     tabbed space is also bad",
        "value": "It cannot have 3 un-escaped"
    }
}

So it should be changed to:

{
    "msg" : {
        "message": "It cannot\ncontain a new-line",
        "description": "Some discription with a\t\ttabbed space",
        "value": "It cannot have 3\4 un-escaped"
    }
}

Which, I should say, makes it quite unreadable in JSON-only format with larger amount of text.

Questions:
Answers:

Hopefully this helps someone else.

My issue was that I had commented HTML in a PHP callback function via AJAX that was parsing the comments and return invalid JSON.

Once I removed the commented HTML, all was good and the JSON was parsed with no issues.

Questions:
Answers:

products is an array which can be used directly:

var i, j;

for(i=0;i<products.length;i++)
  for(j in products[i])
    console.log("property name: " + j,"value: "+products[i][j]);

Questions:
Answers:

Now apparently \r, \b, \t, \f, etc aren’t the only problematic chars that can give you this error.

Note that some browsers may have additional requirements for the input of JSON.parse.

Run this test code on your browser:

var arr = [];
for(var x=0; x < 0xffff; ++x){
    try{
        JSON.parse(String.fromCharCode(0x22, x, 0x22));
    }catch(e){
        arr.push(x);
    }
}
console.log(arr);

Testing on Chrome, I see that it doesn’t allow JSON.parse(String.fromCharCode(0x22, x, 0x22)); where x is 34, 92, or from 0 to 31.

Chars 34 and 92 are the " and \ characters respectively, and they are usually expected and properly escaped. It’s chars 0 to 31 that would give you problems.

To help with debugging, before you do JSON.parse(input), first verify that the input doesn’t contain problematic characters:

function VerifyInput(input){
    for(var x=0; x<input.length; ++x){
        let c = input.charCodeAt(x);
        if(c >= 0 && c <= 31){
            throw 'problematic character found at position ' + x;
        }
    }
}

Questions:
Answers:

Here’s a function I made based on previous replies: it works on my machine but YMMV.

          /**
             * @description Converts a string response to an array of objects.
             * @param {string} string - The string you want to convert.
             * @returns {array} - an array of objects.
            */
            function stringToJson(input) {
              var result = [];

              //replace leading and trailing [], if present
              input = input.replace(/^\[/,'');
              input = input.replace(/\]$/,'');

              //change the delimiter to 
              input = input.replace(/},{/g,'};;;{');

              // preserve newlines, etc - use valid JSON
              //https://stackoverflow.com/questions/14432165/uncaught-syntaxerror-unexpected-token-with-json-parse
            input = input.replace(/\n/g, "\n")  
            .replace(/\'/g, "\'")
            .replace(/\"/g, '\"')
            .replace(/\&/g, "\&")
            .replace(/\r/g, "\r")
            .replace(/\t/g, "\t")
            .replace(/\b/g, "\b")
            .replace(/\f/g, "\f");
            // remove non-printable and other non-valid JSON chars
            input = input.replace(/[\u0000-\u0019]+/g,""); 

              input = input.split(';;;');

              input.forEach(function(element) {
                // console.log(JSON.stringify(element));

                result.push(JSON.parse(element));
              }, this);

              return result;
            }

Questions:
Answers:

Why you need JSON.parse? It’s already in array of object format.

Better use JSON.stringify as below :
var b = JSON.stringify(products);

This may help you.

Questions:
Answers:

Use eval. It takes JavaScript expression/code as string and evaluates/executes it.

eval(inputString);