When working with JavaScript, you'll encounter three ways to declare variables: let, const, and var. While they all serve the same purpose, they behave differently in terms of scoping, mutability, and hoisting. Let's break it down quickly:

1. let:

   • Block-scoped: Meaning it only exists within the nearest block (like a loop or an if statement).
   • Mutable: The value of a variable declared with let can be reassigned.

2. const:

   • Block-scoped like let.
   • Immutable: Once a variable is assigned a value with const, it cannot be reassigned. However, note that the contents of objects or arrays declared with const can still be modified.

3. var:

   • Function-scoped: Unlike let and const, var is scoped to the nearest function block, or global if declared outside of a function.
   • Hoisted: Variables declared with var are moved to the top of their scope during compilation, potentially leading to unexpected results.

Which one should you use?

• Use let when you need to reassign values.
• Use const by default for values that shouldn’t change.
• Avoid var unless you’re dealing with legacy code.

By understanding the nuances of these keywords, you can write cleaner and more predictable code in JavaScript.