Lists all possible prefixes.
This is part of package extra-array.
array.prefixes(x, [n]);
// x: an array
// n: number of values (-1 => any)
const array = require("extra-array");
[...array.prefixes([1, 2])];
// [ [], [ 1 ], [ 1, 2 ] ]
[...array.prefixes([1, 2, 3])];
// [ [], [ 1 ], [ 1, 2 ], [ 1, 2, 3 ] ]