compose an array from a range in js code example

Example 1: range javascript

[...Array(5).keys()];
 => [0, 1, 2, 3, 4]

Example 2: function range() as range js

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;
}