How can I check if a value is a json object?

Question

My server side code returns a value which is a json object on success and a string \'false\' on failure. Now how can I check whether the returned value is a json object?

Answer 1

var checkJSON = function(m) {

   if (typeof m == 'object') { 
      try{ m = JSON.stringify(m); }
      catch(err) { return false; } }

   if (typeof m == 'string') {
      try{ m = JSON.parse(m); }
      catch (err) { return false; } }

   if (typeof m != 'object') { return false; }
   return true;

};


checkJSON(JSON.parse('{}'));      //true
checkJSON(JSON.parse('{"a":0}')); //true
checkJSON('{}');                  //true
checkJSON('{"a":0}');             //true
checkJSON('x');                   //false
checkJSON('');                    //false
checkJSON();                      //false

Answer 2

I don't really like the accepted answer. First and foremost it requires jQuery, which is not always available or required. Secondly, it does a full stringification of the object which to me is overkill. Here's a simple function that thoroughly detects whether a value is JSON-like, using nothing more than a few parts of the lodash library for genericity.

import * as isNull from 'lodash/isNull'
import * as isPlainObject from 'lodash/isPlainObject'
import * as isNumber from 'lodash/isNumber'
import * as isBoolean from 'lodash/isBoolean'
import * as isString from 'lodash/isString'
import * as isArray from 'lodash/isArray'

function isJSON(val) {
  if (isNull(val)
   || isBoolean(val)
   || isString(val))
    return true;
  if (isNumber(val)) 
     return !isNaN(val) && isFinite(val)
  if (isArray(val))
    return Array.prototype.every.call(val, isJSON)
  if (isPlainObject(val)) {
    for (const key of Object.keys(val)) {
      if (!isJSON(val[key]))
        return false
    }
    return true
  }
  return false
}

I've even taken the time to put it up in npm as a package: https://npmjs.com/package/is-json-object. Use it together with something like Webpack to get it in the browser.

Hope this helps someone!

Answer 3

If you have jQuery, use isPlainObject.

if ($.isPlainObject(my_var)) {}

Answer 4

jQuery.parseJSON() should return an object of type "object", if the string was JSON, so you only have to check the type with typeof

var response=jQuery.parseJSON('response from server');
if(typeof response =='object')
{
  // It is JSON
}
else
{
  if(response ===false)
  {
     // the response was a string "false", parseJSON will convert it to boolean false
  }
  else
  {
    // the response was something else
  }
}

Answer 5

You should return json always, but change its status, or in following example the ResponseCode property:

if(callbackResults.ResponseCode!="200"){
    /* Some error, you can add a message too */
} else {
    /* All fine, proceed with code */
};

Answer 6

I am using this to validate JSON Object

function isJsonObject(obj) {
    try {
        JSON.parse(JSON.stringify(obj));
    } catch (e) {
        return false;
    }
    return true;
}

I am using this to validate JSON String

function isJsonString(str) {
    try {
        JSON.parse(str);
    } catch (e) {
        return false;
    }
    return true;
}