In JavaScript, we use both var and let to declare a variable. However, they are not understood the same. The differences between them are scope. var is function scoped while let is block-scoped.
If a variable is defined with let in a later code block, it returns an error of no existing variable, while it returns undefined (declared but no value) with var.
Example of var
console.log(book); var book = 'Learn Flutter'; console.log(book);
Example of let
console.log(book); let book = 'Learn Kotlin'; console.log(book);
