What is typeof() in JavaScript?

Table of Contents

• Introduction
• How typeof() Works in JavaScript
  • Syntax:
  • Example:
• Common Data Types Checked by typeof()
  • 1. Numbers
    • Example:
  • 2. Strings
    • Example:
  • 3. Booleans
    • Example:
  • 4. Undefined
    • Example:
  • 5. Objects
    • Example:
  • 6. Functions
    • Example:
  • 7. Symbols
    • Example:
  • 8. BigInt
    • Example:
• Use Cases for typeof()
  • 1. Type Checking
    • Example:
  • 2. Debugging
  • 3. Conditional Operations
    • Example:
• Conclusion

Introduction

The typeof() operator in JavaScript is used to identify the data type of a given variable or expression. Unlike typical functions, it does not require parentheses to work. The typeof operator returns a string describing the type of the operand passed to it, making it useful for type checking and debugging in JavaScript.

How typeof() Works in JavaScript

The typeof() operator checks the data type of an operand and returns one of several predefined strings representing data types such as "number", "string", "boolean", "undefined", and "object". The operand can be a variable, literal, or expression.

Syntax:

Where operand is the variable or value to be checked.

Example:

Common Data Types Checked by typeof()

1. Numbers

For numeric values (both integers and floating-point numbers), typeof() returns "number".

Example:

2. Strings

When used with string values, typeof() returns "string".

Example:

3. Booleans

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

Example:

4. Undefined

For variables that have been declared but not initialized, typeof() returns "undefined".

Example:

5. Objects

For objects (including arrays and null), typeof() returns "object". However, keep in mind that typeof null is an exception in JavaScript—it also returns "object".

Example:

6. Functions

The typeof() operator returns "function" for functions, allowing you to check whether a variable is callable.

Example:

7. Symbols

For symbols (introduced in ECMAScript 6), typeof() returns "symbol".

Example:

8. BigInt

For BigInt numbers, typeof() returns "bigint".

Example:

Use Cases for typeof()

1. Type Checking

One of the most common uses of typeof() is to verify a variable’s type before performing operations on it.

Example:

2. Debugging

During debugging, developers often use typeof() to check the types of variables and ensure they are what they expect.

3. Conditional Operations

typeof() is helpful in conditionally executing code depending on the type of a variable.

Example:

Conclusion

The typeof() operator in JavaScript is an essential tool for checking variable types, ensuring proper type handling, and aiding in debugging. It supports all the major data types, from strings and numbers to more complex ones like functions and objects. Understanding and using typeof() correctly can help prevent bugs and improve code quality.