What is the difference between let and const in JavaScript?

Table of Contents

• Introduction
• What is let?
  • Definition
  • Characteristics
  • Example
• What is const?
  • Definition
  • Characteristics
  • Example
• Key Differences
• Conclusion

Introduction

In JavaScript, let and const are two modern ways to declare variables, introduced in ES6 (ECMAScript 2015). While both are block-scoped, they serve different purposes regarding variable reassignment. Understanding their differences is crucial for writing clear and effective JavaScript code.

What is let?

Definition

The let keyword is used to declare block-scoped variables that can be reassigned later. It is ideal for variables whose values might change over time.

Characteristics

• Block Scope: Variables declared with let are only accessible within the block they are defined in.
• Reassignment: Variables can be reassigned new values.

Example

What is const?

Definition

The const keyword is used to declare block-scoped variables that cannot be reassigned. It is typically used for constants or variables that should not change throughout the program.

Characteristics

• Block Scope: Similar to let, const variables are only accessible within the block they are defined in.
• No Reassignment: Once a variable is assigned with const, it cannot be reassigned. However, if the variable is an object or array, its properties or elements can still be modified.

Example

Key Differences

1. Reassignment:
   • let: Variables can be reassigned.
   • const: Variables cannot be reassigned once assigned.
2. Use Cases:
   • let: Suitable for variables that will change over time, such as counters or accumulators.
   • const: Best for constants or when you want to ensure that a variable reference remains unchanged.
3. Scope:
   • Both let and const are block-scoped, but const enforces immutability of the variable reference.

Conclusion

In summary, let and const are essential for managing variable scope and immutability in JavaScript. Use let when you expect a variable's value to change, and const when you want to create a constant reference. Understanding these differences will lead to more predictable and maintainable code.