Durstenfeld shuffle

shuffle-durstenfeld.js

// http://en.wikipedia.org/wiki/Fisher-Yates_shuffle#The_modern_algorithm
// https://stackoverflow.com/a/12646864/2684520

// Pre-ES6
/**
 * Randomize array element order in-place.
 * Using Durstenfeld shuffle algorithm.
 */
function shuffleArray(array) {
    for (var i = array.length - 1; i > 0; i--) {
        var j = Math.floor(Math.random() * (i + 1));
        var temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
}

// ES6+
function shuffleArray(array) {
    for (let i = array.length - 1; i > 0; i--) {
        let j = Math.floor(Math.random() * (i + 1));
        [array[i], array[j]] = [array[j], array[i]];
    }
}

I think the ES6 version of that could be just one line; also, I don't think it needs to run in reverse

this:

const durstenshuffeld = (v, r=[...v]) => r.map((x, i, _,  j = ~~(Math.random() * (r.length - i)) + i ) => ([x, r[j]] = [r[j], x], x));

will produce that same shuffle but without destroying the original array

and in ES6, I'm not even certain that inplace-shuffling is necessary; this implementation of the yacht-fisherman algorithm:

    const yacht = (v, r=[...v]) => v.map(() =>
        r.splice(~~(Math.random() * r.length), 1)[0]
    );

is a single line of unbiased, immuted, naive shuffling