JavaScript in and instanceof Operators

Last Updated : 25 Nov, 2024

JavaScript Relational Operators are used to compare their operands and determine the relationship between them. They return a Boolean value (true or false) based on the comparison result.

JavaScript in Operator

The in operator in JavaScript checks if a specified property exists in an object or if an element exists in an array. It returns a Boolean value.

let languages = ["HTML", "CSS", "JavaScript"];
 
// true (index 1 exists in the array)
console.log(1 in languages);
 
// false (index 3 doesn't exist in the array)
console.log(3 in languages);

Output:

true
false

const Data = {
    name: "Rahul",
    age: 21,
    city: "Noida"
};
 
// true ("name" property exists in the object)
console.log("name" in Data);
 
// false ("address" property doesn't exist in the object)
console.log("address" in Data);

Output:

true
false

JavaScript instanceof Operator

The instanceof operator in JavaScript tests if an object is an instance of a particular class or constructor, returning a Boolean value.

let languages = ["HTML", "CSS", "JavaScript"];
 
console.log(languages instanceof Array);
console.log(languages instanceof Object);
console.log(languages instanceof String);
console.log(languages instanceof Number);

Output:

true
true
false
false

let myString = new String();
let myDate = new Date();
 
console.log(myString instanceof Object);
console.log(myString instanceof Date);
console.log(myString instanceof String);
console.log(myDate instanceof Date);
console.log(myDate instanceof Object);
console.log(myDate instanceof String);

Output:

true
false
true
true
true
false

Javascript Unary Operators Javascript If-Else