In which scenario is it preferable to use `let` instead of `var`?

Using let is preferable when you need block scope for your variables. In JavaScript, var declares a variable that is function-scoped or globally-scoped, depending on where it is declared. This can lead to unintended behavior, especially in situations like loops or conditional statements, where you might want a variable to maintain its value only within a specific block of code.

For example, if you declare a loop variable using var, it will be accessible outside the loop after the loop has completed. In contrast, if you use let, the variable will be confined to the block in which it was declared, preventing access from outside that block. This allows for better control over variable lifetimes and helps prevent bugs associated with variable scope.

Using let enhances code readability and maintainability by making it clear which parts of your code can interact with the variable. This is particularly useful in scenarios like closures or when dealing with asynchronous code, as it helps avoid unintended references to a variable that has changed during execution.