Learn how JavaScript’s built-in functions like map() and filter(), as well as compose() and chain(), support a more elegant handling of JavaScript arrays.

The array forEach method takes a callback (function) as a parameter, where you can pass in the value and index of the current array position; numbers.forEach((number, index) => {...}); Inside the body ...

Array objects cannot use arbitrary strings as element indexes (as in an associative array) but must use nonnegative integers (or their respective string form). Setting or accessing via non-integers ...