What is the significance of the key attribute in React, and when would you use it?

There are 3 ways to declare variables in JavaScript. So, to compare them I have a few points:

1. Mutability: let is mutable, and its value can be changed. const is immutable after initialization, meaning it cannot be reassigned.
2. Scope: let and const are block-scoped, confined to the block (e.g., inside an if statement or a loop) in which they are defined. On the other hand, var is function-scoped or globally scoped, not having block-level scope.
3. Hoisting: When let and const are hoisted without a default initialization, accessing them before the line they are declared throws a ReferenceError. In contrast, var declarations are hoisted and initialized with undefined, allowing them to be accessed before the declaration line without throwing an error.
4. Redeclaration: var can be redeclared within the same scope, while let and const cannot be redeclared in the same scope.