let vs const
`const` is a signal that the identifier won't be reassigned.
`let` is a signal that the variable may be reassigned, such as a counter in a
loop, or a value swap in an algorithm.
It also signals that the variable will be used only in the block it's defined
in, which is not always the entire containing function.
// var declares a variable, meaning its value will vary.
// const declares a constant, meaning its value will remain
// consistant and not change.
// If your variable changes throughout the program or website,
// declare it using a var statement.
// Otherwise, if its value does not change, declare it using
// a const statement.
const myConst='A const does not change.';
var myVar='A var does change.';
var myVar=2;