[...Array(5).keys()]; => [0, 1, 2, 3, 4]
[...Array(10).keys()] //=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
function range(start, end) { /* generate a range : [start, start+1, ..., end-1, end] */ var len = end - start + 1; var a = new Array(len); for (let i = 0; i < len; i++) a[i] = start + i; return a; }
arr.fill(value[, start[, end]])