JSON, or JavaScript Object Notation, is a ubiquitous data format used by all sorts of mobile and web apps for asynchronous browser-server communication. JSON is an extremely popular data format, very easy to work with, compatible with every major programming language, and is supported by every major browser. However, just like any programming language, it throws a lot of errors when it decides that today is not going to be your day.

JSON.Parse Syntax Errors

In most web applications, nearly all data transferred from a web server is transmitted in a string format. To convert that string into JSON, we use the JSON.parse() function, and this is the main function that throws errors. Nearly all JSON.parse errors are a subset of the SyntaxError error type. The debugging console throws around 32 different error messages when you mess up your JSON data. And some of them are very tricky to debug; and yes I am talking about you unexpected non-whitespace character after JSON data.

Why the SyntaxError Horror?

SyntaxError is an inherited object of the main error object The main reason behind the error is usually a mistake in the JSON file syntax. You mess up and put a “ instead of a ‘ and you invite to face the SyntaxError JSON.parse: unexpected character.

Just like every programming language, a JSON file has a fixed syntax. Small syntax errors throws errors. For example, in the following code, I forgot to remove a trailing comma

JSON.parse('[a,b, c, d, e, f,]');

Similarly, in this example, I forgot to add the final } character.

JSON.parse('{"LambdaTest": 1,');

How to Catch the Error Before Hand

The problem with debugging JSON errors is that you only get to know about one error at a time. Debuggers throw the first error they find and then stop. It would be up to you to regression find the bugs. Usually, it’s not as difficult as it sounds.

The first step is to make sure that your JSON file is perfect from the get go. Here you can take help from JSON linting tools like cleverly named jsonlint.com

If you don’t have any control over the receiving JSON file, then the next step is to add catch exceptions around your JSON.parse.

function validatingJSON (json) {

  var checkedjson

  try {
    checkedjson = JSON.parse(json)
  } catch (e) {

  }

  return checkedjson }

Also, here are the main errors related to JSON.parse that I very painstakingly collected from a very single source [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/JSON_bad_parse]:

SyntaxError: JSON.parse: unterminated string literal 
SyntaxError: JSON.parse: bad control character in string literal 
SyntaxError: JSON.parse: bad character in string literal 
SyntaxError: JSON.parse: bad Unicode escape 
SyntaxError: JSON.parse: bad escape character 
SyntaxError: JSON.parse: unterminated string 
SyntaxError: JSON.parse: no number after minus sign 
SyntaxError: JSON.parse: unexpected non-digit 
SyntaxError: JSON.parse: missing digits after decimal point 
SyntaxError: JSON.parse: unterminated fractional number 
SyntaxError: JSON.parse: missing digits after exponent indicator 
SyntaxError: JSON.parse: missing digits after exponent sign 
SyntaxError: JSON.parse: exponent part is missing a number 
SyntaxError: JSON.parse: unexpected end of data 
SyntaxError: JSON.parse: unexpected keyword 
SyntaxError: JSON.parse: unexpected character 
SyntaxError: JSON.parse: end of data while reading object contents 
SyntaxError: JSON.parse: expected property name or '}' 
SyntaxError: JSON.parse: end of data when ',' or ']' was expected 
SyntaxError: JSON.parse: expected ',' or ']' after array element 
SyntaxError: JSON.parse: end of data when property name was expected 
SyntaxError: JSON.parse: expected double-quoted property name 
SyntaxError: JSON.parse: end of data after property name when ':' was expected 
SyntaxError: JSON.parse: expected ':' after property name in object 
SyntaxError: JSON.parse: end of data after property value in object 
SyntaxError: JSON.parse: expected ',' or '}' after property value in object 
SyntaxError: JSON.parse: expected ',' or '}' after property-value pair in object literal 
SyntaxError: JSON.parse: property names must be double-quoted strings 
SyntaxError: JSON.parse: expected property name or '}' 
SyntaxError: JSON.parse: unexpected character 
SyntaxError: JSON.parse: unexpected non-whitespace character after JSON data

If this doesn’t help, then you are in for one long debugging session.