What is the typeof operator in JavaScript?

Table of Contents

• Introduction
• Syntax of typeof
  • Example:
• How typeof Works
  • 1. Number
    • Example:
  • 2. String
    • Example:
  • 3. Boolean
    • Example:
  • 4. Undefined
    • Example:
  • 5. Object
    • Example:
  • 6. Function
    • Example:
  • 7. Symbol
    • Example:
  • 8. BigInt
    • Example:
• Common Use Cases of typeof
• Conclusion

Introduction

The typeof operator in JavaScript is used to determine the data type of a given variable or value. It is a unary operator, meaning it takes only one operand, and it returns a string indicating the type of the evaluated expression. This operator is extremely useful for debugging and type-checking.

Syntax of typeof

The syntax for using the typeof operator is simple:

Here, operand is the value or variable whose type you want to check.

Example:

How typeof Works

The typeof operator checks the data type of the operand and returns the type as a string. Below are some common data types and what typeof will return for each:

1. Number

For numbers, whether integer or floating point, typeof returns "number".

Example:

2. String

For strings, typeof returns "string".

Example:

3. Boolean

For boolean values (true or false), typeof returns "boolean".

Example:

4. Undefined

For variables that are declared but not assigned a value, typeof returns "undefined".

Example:

5. Object

For objects, arrays, and null, typeof returns "object". However, keep in mind that there is a known quirk in JavaScript: typeof null also returns "object".

Example:

6. Function

For functions, typeof returns "function", making it easy to check if a variable is callable.

Example:

7. Symbol

For symbols, introduced in ES6, typeof returns "symbol".

Example:

8. BigInt

For BigInt numbers, typeof returns "bigint".

Example:

Common Use Cases of typeof

• Type Checking: You can use typeof to ensure that a variable is of the correct type before performing an operation.

  Example:

• Debugging: While debugging, typeof helps verify the type of variables and pinpoint issues.

Conclusion

The typeof operator in JavaScript is a powerful tool for determining the type of a value or variable. It supports all basic data types such as numbers, strings, booleans, and even more complex types like functions and symbols. Understanding how typeof works can help ensure that your code handles data correctly and effectively.