Javascript: Check if a variable is an Object

This article shows how you can check if a Javascript variable is of an Object type.

There are different ways to check if a variable is an Object in Javascript.

1) First way

// define an object
var myObject = {id: 11, name: John}

console.log(Object.prototype.toString.call(myObject)); // [object Object]

// check if the variable is an object
if (Object.prototype.toString.call(myObject) === '[object Object]') {
    console.log('The variable is an object.');
} else {
    console.log('The variable is NOT an object.');
}

// for array, you will get [object Array]
var myArray = [1, 2, 3];
console.log(Object.prototype.toString.call(myArray)); // [object Array]

2) Second way

We use typeof to check the type of the variable.

We also check for Array using isArray() function because both Array and Object has typeof = object.

Array.isArray() method was introduced in ECMAscript 5 (ES5).

function isObject(obj) {
  return obj !== null && typeof obj === 'object' && Array.isArray(obj) === false;
}

console.log(isObject(myObject)); // true

var myArray = [1, 2, 3];
console.log(isObject(myArray)); // false

3) Third way

Using instanceof operator

// using object instanceof and constructor operator
function isObject(obj) {
  return obj instanceof Object && obj.constructor === Object;
}

console.log(isObject(myObject)); // true
console.log(isObject(myArray)); // false

Using typeof operator

// using object typeof and constructor operator
function isObject(obj) {
  return typeof obj === 'object' && obj.constructor === Object;
}

console.log(isObject(myObject)); // true
console.log(isObject(myArray)); // false

Here’s the difference between typeof and instanceof:

instanceof operator tests the presence of constructor.prototype in object’s prototype chain.

typeof operator returns a string indicating the type of the operand. The operand can be an object or primitive value like string, number, null, undefined, etc.

const a = "Primitive String";
const b = new String("String Object");

console.log(typeof a); // output: string
console.log(typeof b); // output: object

console.log(a instanceof String); // output: false
console.log(b instanceof String); // output: true

Hope this helps. Thanks.