Array indexing and length

Each value in an array has a unique position, called an index.

Indexes start at 0 for the first element (this is called zero indexing). The length of an array can be accessed with the length property, which allows for a common programming pattern where a for loop is used to iterate over the elements of an array.

Notice that the index of the last element of an array is array.length - 1. For example, if we wanted to extend the program above to calculate any length of the Fibonacci sequence, we could use a while loop to keep appending new items.