Skip to content

Instantly share code, notes, and snippets.

What would you like to do?
* range()
* Returns an array of numbers between a start number and an end number incremented
* sequentially by a fixed number(step), beginning with either the start number or
* the end number depending on which is greater.
* @param {number} start (Required: The start number.)
* @param {number} end (Required: The end number. If end is less than start,
* then the range begins with end instead of start and decrements instead of increment.)
* @param {number} step (Optional: The fixed increment or decrement step. Defaults to 1.)
* @return {array} (An array containing the range numbers.)
* @throws {TypeError} (If any of start, end and step is not a finite number.)
* @throws {Error} (If step is not a positive number.)
function range(start, end, step = 1) {
// Test that the first 3 arguments are finite numbers.
// Using Array.prototype.every() and Number.isFinite().
const allNumbers = [start, end, step].every(Number.isFinite);
// Throw an error if any of the first 3 arguments is not a finite number.
if (!allNumbers) {
throw new TypeError('range() expects only finite numbers as arguments.');
// Ensure the step is always a positive number.
if (step <= 0) {
throw new Error('step must be a number greater than 0.');
// When the start number is greater than the end number,
// modify the step for decrementing instead of incrementing.
if (start > end) {
step = -step;
// Determine the length of the array to be returned.
// The length is incremented by 1 after Math.floor().
// This ensures that the end number is listed if it falls within the range.
const length = Math.floor(Math.abs((end - start) / step)) + 1;
// Fill up a new array with the range numbers
// using Array.from() with a mapping function.
// Finally, return the new array.
return Array.from(Array(length), (x, index) => start + index * step);
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment