How to check if a value is object-like in JavaScript ?

In JavaScript, objects are a collection of related data. It is also a container for name-value pairs. In JavaScript, we can check the type of value in many ways. Basically, we check if a value is object-like using typeof, instanceof, constructor, and Object.prototype.toString.call(k). All of the operators are used in some specific conditions.

typeof operator: This is used to identify the type of variable. It returns a variable type. It is the easiest way to check the type of the variable. It works for some variables, but it did not identify the exact type of variable.

Conditions: It treated array, set, and null same as the object. typeof returns object for all of these. In the case of variable except three of this typeof is used.

• Syntax: 

typeof VariableName; 

• Example:

Javascript

<script>

  let k = {Name:'gfg',Country:'India'};
  let k0 = new Set()
  let k1 = [1,2,3];
  let k2 = "hello";
  let k3 = null ;
  let k4 = undefined;

  console.log( typeof k  )
  console.log( typeof k0  )
  console.log( typeof k1  )
  console.log( typeof k2  )
  console.log( typeof k3  )
  console.log( typeof k4  )

</script>

Output:

object
object 
object
string 
object
undefined

instanceof operator: This is used to check if any instance is made with a certain constructor or not. It returns true if it is made with constructor else returns false. It only works for those who are wrapped in regular object types.

Condition: It treats the array and sets the same as the object. So we can use instanceof operator for all values except these two.

• Syntax:

Variable instanceof object;

• Example:

Javascript

<script>

  let k = {Name:'gfg',Country:'India'};
  let k0 = new Set()
  let k1 = [1,2,3];
  let k2 = "hello";
  let k3 = null ;
  let k4 = undefined;

  console.log( k   instanceof Object)
  console.log( k0   instanceof Object)
  console.log( k1  instanceof Object)
  console.log( k2  instanceof Object)
  console.log( k3  instanceof Object)
  console.log( k4  instanceof Object)

</script>

Output:

True 
True 
True
false 
false 
false

constructor property: This is the property of the variable which points to the fundamental object constructor type of that object. We can check for those variables which have constructor property. 

Condition: The constructor method throw an error for variables not having constructor property. null and undefined don’t have constructor property, so it throws an error.

• Syntax: 

Variable.constructor === Object 

• Example:

Javascript

<script>

  let k = {Name:'gfg',Country:'India'};
  let k0 = new Set()
  let k1 = [1,2,3];
  let k2 = "hello";

  console.log( k.constructor === Object)
  console.log( k0.constructor === Object)
  console.log( k1.constructor === Object)
  console.log( k2.constructor === Object)

<script>

Output:

True 
false 
false 
false