How to check if JavaScript object is JSON
JavascriptJsonJavascript Problem Overview
I have a nested JSON object that I need to loop through, and the value of each key could be a String, JSON array or another JSON object. Depending on the type of object, I need to carry out different operations. Is there any way I can check the type of the object to see if it is a String, JSON object or JSON array?
I tried using typeof and instanceof but both didn't seem to work, as typeof will return an object for both JSON object and array, and instanceof gives an error when I do obj instanceof JSON.
To be more specific, after parsing the JSON into a JS object, is there any way I can check if it is a normal string, or an object with keys and values (from a JSON object), or an array (from a JSON array)?
For example:
JSON
var data = "{'hi':
{'hello':
['hi1','hi2']
},
'hey':'words'
}";
Sample JavaScript
var jsonObj = JSON.parse(data);
var path = ["hi","hello"];
function check(jsonObj, path) {
var parent = jsonObj;
for (var i = 0; i < path.length-1; i++) {
var key = path[i];
if (parent != undefined) {
parent = parent[key];
}
}
if (parent != undefined) {
var endLength = path.length - 1;
var child = parent[path[endLength]];
//if child is a string, add some text
//if child is an object, edit the key/value
//if child is an array, add a new element
//if child does not exist, add a new key/value
}
}
How do I carry out the object checking as shown above?
Javascript Solutions
Solution 1 - Javascript
I'd check the constructor attribute.
e.g.
var stringConstructor = "test".constructor;
var arrayConstructor = [].constructor;
var objectConstructor = ({}).constructor;
function whatIsIt(object) {
if (object === null) {
return "null";
}
if (object === undefined) {
return "undefined";
}
if (object.constructor === stringConstructor) {
return "String";
}
if (object.constructor === arrayConstructor) {
return "Array";
}
if (object.constructor === objectConstructor) {
return "Object";
}
{
return "don't know";
}
}
var testSubjects = ["string", [1,2,3], {foo: "bar"}, 4];
for (var i=0, len = testSubjects.length; i < len; i++) {
alert(whatIsIt(testSubjects[i]));
}
Edit: Added a null check and an undefined check.
Solution 2 - Javascript
You can use Array.isArray to check for arrays. Then typeof obj == 'string', and typeof obj == 'object'.
var s = 'a string', a = [], o = {}, i = 5;
function getType(p) {
if (Array.isArray(p)) return 'array';
else if (typeof p == 'string') return 'string';
else if (p != null && typeof p == 'object') return 'object';
else return 'other';
}
console.log("'s' is " + getType(s));
console.log("'a' is " + getType(a));
console.log("'o' is " + getType(o));
console.log("'i' is " + getType(i));
> 's' is string
'a' is array
'o' is object
'i' is other
Solution 3 - Javascript
An JSON object is an object. To check whether a type is an object type, evaluate the constructor property.
function isObject(obj)
{
return obj !== undefined && obj !== null && obj.constructor == Object;
}
The same applies to all other types:
function isArray(obj)
{
return obj !== undefined && obj !== null && obj.constructor == Array;
}
function isBoolean(obj)
{
return obj !== undefined && obj !== null && obj.constructor == Boolean;
}
function isFunction(obj)
{
return obj !== undefined && obj !== null && obj.constructor == Function;
}
function isNumber(obj)
{
return obj !== undefined && obj !== null && obj.constructor == Number;
}
function isString(obj)
{
return obj !== undefined && obj !== null && obj.constructor == String;
}
function isInstanced(obj)
{
if(obj === undefined || obj === null) { return false; }
if(isArray(obj)) { return false; }
if(isBoolean(obj)) { return false; }
if(isFunction(obj)) { return false; }
if(isNumber(obj)) { return false; }
if(isObject(obj)) { return false; }
if(isString(obj)) { return false; }
return true;
}
Solution 4 - Javascript
If you are trying to check the type of an object after you parse a JSON string, I suggest checking the constructor attribute:
obj.constructor == Array || obj.constructor == String || obj.constructor == Object
This will be a much faster check than typeof or instanceof.
If a JSON library does not return objects constructed with these functions, I would be very suspiciouse of it.
Solution 5 - Javascript
you can also try to parse the data and then check if you got object:
try {
var testIfJson = JSON.parse(data);
if (typeof testIfJson == "object"){
//Json
} else {
//Not Json
}
}
catch {
return false;
}
Solution 6 - Javascript
The answer by @PeterWilkinson didn't work for me because a constructor for a "typed" object is customized to the name of that object. I had to work with typeof
function isJson(obj) {
var t = typeof obj;
return ['boolean', 'number', 'string', 'symbol', 'function'].indexOf(t) == -1;
}
Solution 7 - Javascript
You could make your own constructor for JSON parsing:
var JSONObj = function(obj) { $.extend(this, JSON.parse(obj)); }
var test = new JSONObj('{"a": "apple"}');
//{a: "apple"}
Then check instanceof to see if it needed parsing originally
test instanceof JSONObj
Solution 8 - Javascript
I wrote an npm module to solve this problem. It's available here:
object-types: a module for finding what literal types underly objects
Install
npm install --save object-types
Usage
const objectTypes = require('object-types');
objectTypes({});
//=> 'object'
objectTypes([]);
//=> 'array'
objectTypes(new Object(true));
//=> 'boolean'
Take a look, it should solve your exact problem. Let me know if you have any questions! https://github.com/dawsonbotsford/object-types
Solution 9 - Javascript
Why not check Number - a bit shorter and works in IE/Chrome/FF/node.js
function whatIsIt(object) {
if (object === null) {
return "null";
}
else if (object === undefined) {
return "undefined";
}
if (object.constructor.name) {
return object.constructor.name;
}
else { // last chance 4 IE: "\nfunction Number() {\n [native code]\n}\n" / node.js: "function String() { [native code] }"
var name = object.constructor.toString().split(' ');
if (name && name.length > 1) {
name = name[1];
return name.substr(0, name.indexOf('('));
}
else { // unreachable now(?)
return "don't know";
}
}
}
var testSubjects = ["string", [1,2,3], {foo: "bar"}, 4];
// Test all options
console.log(whatIsIt(null));
console.log(whatIsIt());
for (var i=0, len = testSubjects.length; i < len; i++) {
console.log(whatIsIt(testSubjects[i]));
}
Solution 10 - Javascript
I combine the typeof operator with a check of the constructor attribute (by Peter):
var typeOf = function(object) {
var firstShot = typeof object;
if (firstShot !== 'object') {
return firstShot;
}
else if (object.constructor === [].constructor) {
return 'array';
}
else if (object.constructor === {}.constructor) {
return 'object';
}
else if (object === null) {
return 'null';
}
else {
return 'don\'t know';
}
}
// Test
var testSubjects = [true, false, 1, 2.3, 'string', [4,5,6], {foo: 'bar'}, null, undefined];
console.log(['typeOf()', 'input parameter'].join('\t'))
console.log(new Array(28).join('-'));
testSubjects.map(function(testSubject){
console.log([typeOf(testSubject), JSON.stringify(testSubject)].join('\t\t'));
});
Result:
typeOf() input parameter
---------------------------
boolean true
boolean false
number 1
number 2.3
string "string"
array [4,5,6]
object {"foo":"bar"}
null null
undefined
Solution 11 - Javascript
I know this is a very old question with good answers. However, it seems that it's still possible to add my 2¢ to it.
Assuming that you're trying to test not a JSON object itself but a String that is formatted as a JSON (which seems to be the case in your var data), you could use the following function that returns a boolean (is or is not a 'JSON'):
function isJsonString( jsonString ) {
// This function below ('printError') can be used to print details about the error, if any.
// Please, refer to the original article (see the end of this post)
// for more details. I suppressed details to keep the code clean.
//
let printError = function(error, explicit) {
console.log(`[${explicit ? 'EXPLICIT' : 'INEXPLICIT'}] ${error.name}: ${error.message}`);
}
try {
JSON.parse( jsonString );
return true; // It's a valid JSON format
} catch (e) {
return false; // It's not a valid JSON format
}
}
Here are some examples of using the function above:
console.log('\n1 -----------------');
let j = "abc";
console.log( j, isJsonString(j) );
console.log('\n2 -----------------');
j = `{"abc": "def"}`;
console.log( j, isJsonString(j) );
console.log('\n3 -----------------');
j = '{"abc": "def}';
console.log( j, isJsonString(j) );
console.log('\n4 -----------------');
j = '{}';
console.log( j, isJsonString(j) );
console.log('\n5 -----------------');
j = '[{}]';
console.log( j, isJsonString(j) );
console.log('\n6 -----------------');
j = '[{},]';
console.log( j, isJsonString(j) );
console.log('\n7 -----------------');
j = '[{"a":1, "b": 2}, {"c":3}]';
console.log( j, isJsonString(j) );
When you run the code above, you will get the following results:
1 -----------------
abc false
2 -----------------
{"abc": "def"} true
3 -----------------
{"abc": "def} false
4 -----------------
{} true
5 -----------------
[{}] true
6 -----------------
[{},] false
7 -----------------
[{"a":1, "b": 2}, {"c":3}] true
Please, try the snippet below and let us know if this works for you. :)
IMPORTANT: the function presented in this post was adapted from https://airbrake.io/blog/javascript-error-handling/syntaxerror-json-parse-bad-parsing where you can find more and interesting details about the JSON.parse() function.
function isJsonString( jsonString ) {
let printError = function(error, explicit) {
console.log(`[${explicit ? 'EXPLICIT' : 'INEXPLICIT'}] ${error.name}: ${error.message}`);
}
try {
JSON.parse( jsonString );
return true; // It's a valid JSON format
} catch (e) {
return false; // It's not a valid JSON format
}
}
console.log('\n1 -----------------');
let j = "abc";
console.log( j, isJsonString(j) );
console.log('\n2 -----------------');
j = `{"abc": "def"}`;
console.log( j, isJsonString(j) );
console.log('\n3 -----------------');
j = '{"abc": "def}';
console.log( j, isJsonString(j) );
console.log('\n4 -----------------');
j = '{}';
console.log( j, isJsonString(j) );
console.log('\n5 -----------------');
j = '[{}]';
console.log( j, isJsonString(j) );
console.log('\n6 -----------------');
j = '[{},]';
console.log( j, isJsonString(j) );
console.log('\n7 -----------------');
j = '[{"a":1, "b": 2}, {"c":3}]';
console.log( j, isJsonString(j) );
Solution 12 - Javascript
Try this
if ( typeof is_json != "function" )
function is_json( _obj )
{
var _has_keys = 0 ;
for( var _pr in _obj )
{
if ( _obj.hasOwnProperty( _pr ) && !( /^\d+$/.test( _pr ) ) )
{
_has_keys = 1 ;
break ;
}
}
return ( _has_keys && _obj.constructor == Object && _obj.constructor != Array ) ? 1 : 0 ;
}
It works for the example below
var _a = { "name" : "me",
"surname" : "I",
"nickname" : {
"first" : "wow",
"second" : "super",
"morelevel" : {
"3level1" : 1,
"3level2" : 2,
"3level3" : 3
}
}
} ;
var _b = [ "name", "surname", "nickname" ] ;
var _c = "abcdefg" ;
console.log( is_json( _a ) );
console.log( is_json( _b ) );
console.log( is_json( _c ) );
Solution 13 - Javascript
Based on @Martin Wantke answer, but with some recommended improvements/adjusts...
// NOTE: Check JavaScript type. By Questor
function getJSType(valToChk) {
function isUndefined(valToChk) { return valToChk === undefined; }
function isNull(valToChk) { return valToChk === null; }
function isArray(valToChk) { return valToChk.constructor == Array; }
function isBoolean(valToChk) { return valToChk.constructor == Boolean; }
function isFunction(valToChk) { return valToChk.constructor == Function; }
function isNumber(valToChk) { return valToChk.constructor == Number; }
function isString(valToChk) { return valToChk.constructor == String; }
function isObject(valToChk) { return valToChk.constructor == Object; }
if(isUndefined(valToChk)) { return "undefined"; }
if(isNull(valToChk)) { return "null"; }
if(isArray(valToChk)) { return "array"; }
if(isBoolean(valToChk)) { return "boolean"; }
if(isFunction(valToChk)) { return "function"; }
if(isNumber(valToChk)) { return "number"; }
if(isString(valToChk)) { return "string"; }
if(isObject(valToChk)) { return "object"; }
}
NOTE: I found this approach very didactic, so I submitted this answer.
Solution 14 - Javascript
Try, Catch block will help you to solve this
Make a function
function IsJson(str) {
try {
JSON.parse(str);
} catch (e) {
return false;
}
return true;
}
Example:
console.log(IsJson('abc')) // false
console.log(IsJson('[{"type":"email","detail":"[email protected]"}]')) // true
Solution 15 - Javascript
Peter's answer with an additional check! Of course, not 100% guaranteed!
var isJson = false;
outPutValue = ""
var objectConstructor = {}.constructor;
if(jsonToCheck.constructor === objectConstructor){
outPutValue = JSON.stringify(jsonToCheck);
try{
JSON.parse(outPutValue);
isJson = true;
}catch(err){
isJson = false;
}
}
if(isJson){
alert("Is json |" + JSON.stringify(jsonToCheck) + "|");
}else{
alert("Is other!");
}
Solution 16 - Javascript
I have a pretty lazy answer to this, which will not throw an error if you try to parse a string/other values.
const checkForJson = (value) => {
if (typeof value !== "string") return false;
return value[0] === "{" && value[value.length - 1] === "}";
}
You can use this to check the value of your keys while you make some recursive func; sorry if this doesn't answer the question completely
Ofc this isn't the most elegant solution and will fail when a string actually starts with "{" and ends with "}" although those use cases would be rare, and if you really wanted, you can check for a presence of quotes or other nonsense... anyway, use at your own discretion.
TLDR: it's not bulletproof, but it's simple and works for the vast majority of use cases.
Solution 17 - Javascript
lodash is also the best bet to check these things.
function Foo() {
this.a = 1;
}
_.isPlainObject(new Foo);
// => false
_.isPlainObject([1, 2, 3]);
// => false
_.isPlainObject({ 'x': 0, 'y': 0 });
// => true
_.isPlainObject(Object.create(null));
// => true
https://www.npmjs.com/package/lodash
https://lodash.com/docs/#isPlainObject
Solution 18 - Javascript
Quickly check for a JSON structure using lodash-contrib:
const _ = require('lodash-contrib');
_.isJSON('{"car": "ferarri"}'); //true for stringified
_.isJSON({car: "ferarri"}); //true
Usage guide: this blog entry
Solution 19 - Javascript
try this dirty way
('' + obj).includes('{')