When should we use "const " and when should we use "let"?

In JavaScript, both const and let are used to declare variables, but they have some important differences:

1. When to use const?

const is used when you want to declare a variable that will not be reassigned.

This doesn't mean the value it holds must be a constant or immutable, but the variable identifier itself cannot be reassigned to a new value.

For example:

// Declaring a function with const
const addNumbers = (n1, n2) => n1 + n2;  

// This line would cause an error
// addNumbers = (n1, n2) => n1 - n2;

Since addNumbers is a function defined as const, you can't later assign it a different function.

2. When to use let?

let is more flexible. It allows you to declare a variable and change its value later.

This is useful when dealing with values that might change over time, or if you want to reassign the variable with new data, as seen with the result variable:

let result = addNumbers(2, 5);
console.log(result);  // Output: 7

// Reassign result with a new calculation
result = addNumbers(10, 15);
console.log(result);  // Output: 25

So, in general:

• Use const for variables that you don't want to reassign, like function definitions or constants.

• Use let when you expect a variable's value to change.

Hope this helps! Let me know if you have more questions.