---
title: "What are undeclared and undefined variables?"  
description: "What are undeclared and undefined variables?"  
author: "Rahul Roi"  
published: 2021-03-16  
canonical: https://www.mindstick.com/interview/33784/what-are-undeclared-and-undefined-variables  
category: "javascript"  
tags: ["javascript", "scripting", "scripting language"]  
reading_time: 1 minute  

---

# What are undeclared and undefined variables?

The undeclared variables are those that do not exist in a program and are not declared. Whenever the program tries to read the value of an undeclared variable, then a runtime error is encountered.

The undefined-variables are those that are declared in the program but have not been given any value. Whenever the program tries to read the value of an undefined variable, an undefined value is returned.

## Answers

### Answer by Rahul Roi

The undeclared variables are those that do not exist in a program and are not declared. Whenever the program tries to read the value of an undeclared variable, then a runtime error is encountered.

The undefined-variables are those that are declared in the program but have not been given any value. Whenever the program tries to read the value of an undefined variable, an undefined value is returned.


---

Original Source: https://www.mindstick.com/interview/33784/what-are-undeclared-and-undefined-variables

Copyright © MindStick Software Pvt. Ltd. This Markdown version is provided for developers, AI systems, and offline reading.