From: Mischa POSLAWSKY <perl@shiar.org>
Date: Wed, 29 Dec 2021 05:04:34 +0000 (+0100)
Subject: word/quiz: fisher-yates shuffle algorithm
X-Git-Tag: v1.13~65
X-Git-Url: http://git.shiar.nl/sheet.git/commitdiff_plain/26074080358f5993e59f19526704c58c1de2606f

word/quiz: fisher-yates shuffle algorithm

Fixes very bad randomisation in some browsers.

Reference: <https://javascript.info/array-methods#shuffle-an-array>
---

diff --git a/word/quiz.js b/word/quiz.js
index 70f8500..361d075 100644
--- a/word/quiz.js
+++ b/word/quiz.js
@@ -1,5 +1,9 @@
 Array.prototype.shuffle = function () {
-	return this.sort(() => {return .5 - Math.random()});
+	for (let i = this.length - 1; i > 0; i--) {
+		const j = Math.floor(Math.random() * (i + 1)); // random index 0..i
+		[this[i], this[j]] = [this[j], this[i]]; // swap elements
+	}
+	return this;
 };
 
 class WordQuiz {