How to Check Type in JavaScript

JavaScript is a language that allows us to assign values to the variables at the run time. In the same way, the ability to determine variable types and value types becomes significant when programming. However, numerous ways of handling this in JavaScript can guarantee a variable is of a certain type or has a defined value. In the present article, we will explore them and provide you with relevant examples and explanations through the research paper.

Key Points on Type Checking in JavaScript:

• The typeof operator is used to check the type of primitive data types like numbers, strings, and booleans.
• instanceof is used to check the type of objects or instances of classes.
• In JavaScript, arrays and null values are special cases when using typeof.
• Constructor Functions can also be used to check the type of objects.
• Type checking is crucial when validating input or ensuring correct variable usage.

Methods to Check Type:

Using typeof

The typeof operator returns a string indicating the type of a variable. It's widely used to check primitive data types.

let num = 42;
console.log(typeof num); // Output: number
            
let str = "Hello, JavaScript!";
console.log(typeof str); // Output: string

Using instanceof

The instanceof operator checks whether an object is an instance of a particular class or constructor function.

let date = new Date();
console.log(date instanceof Date); // Output: true
            
let arr = [1, 2, 3];
console.log(arr instanceof Array); // Output: true

Handling Special Cases: typeof null and Arrays

Using typeof on a null value returns "object", and arrays are also considered objects. For arrays, you can use Array.isArray() to specifically check for arrays.

let empty = null;
console.log(typeof empty); // Output: object
            
let arr = [1, 2, 3];
console.log(Array.isArray(arr)); // Output: true