JS: Range Function for Array

By Xah Lee. Date: . Last updated: .

There's no builtin range function to creat a array.

0 Index Based Range Function

The easiest way to create a array from 0 to n is:

[... Array(n).keys()]

Here's how it works:

Array(n) [see Array Constructor] creates a Sparse Array of n elements. .keys() [see Array.prototype.keys] return its indexes, as a iterable object. The Spread Operator ... wrapped with square bracket makes it an actual array.

General Range Function

Here's a general range function.

/* [
xah_range(min, max) β†’ return a array from min to max, inclusive.
xah_range(min, max, step) β†’ in steps of step.
If step is not integer, then max may not be included.
http://xahlee.info/js/javascript_range_array.html
version 2019-10-31
] */
const xah_range = (( min, max, step = 1, ) => (Array(Math.floor((max - min) / step) + 1).fill(min).map( ((x, i) => (x + i * step)), )));

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