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At the moment, I have some code to pick one random object from an array and it works well. However, I don't want any repeats in the output. I want to randomly provide a new site link on the click of a button, and it should be different every time (until of course we run out of objects in the array). What code can I add to this to prevent any repetition?

Here's the sample code:

<script> var links = [ "page-1", "page-2", "page-3", // ... "page-108", ] function openSite() { var randIdx = Math.random() * links.length; randIdx = parseInt(randIdx, 10); var link = 'https://websitename.com/page/' + links[randIdx]; window.location.assign(link); }; </script>
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    Store the generated index and check against it every time a new random number is generated. When out of the item, you can reset or anything you like. Commented Aug 19, 2020 at 12:29
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    Is removing the element out of the array an option? This would mean the array need to be refilled when you ran out of items. Commented Aug 19, 2020 at 12:31
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    Does this answer your question? How to randomize (shuffle) a JavaScript array? Commented Aug 19, 2020 at 12:32
  • Hum ! You need something that holds the indexes that have been already visited. Commented Aug 19, 2020 at 13:03
  • If you refer to different HTTP requests, then you need to store used values somewhere (a database, LocalStorage, whatever). Commented Aug 19, 2020 at 13:55

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There are different ways of solving this problem.

One would be to make a "shuffled" copy of your array, and then, instead of picking a random item from the original array, you pick an item from the shuffled array in sequence. There are also different algorithms for shuffling an array. You can find some here: How to randomize (shuffle) a JavaScript array?.

Another option would be to make a copy of your array, and every time you pick an item, you remove it from the copy array, and then you use the copy array length to find the index of the next random item.

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An option is to

  1. shuffle the array, see here for a good shuffling algorithm
  2. repeatedly use links.pop() to remove and return the last item until its empty

eg

links = shuffle(links) for (let i=0, L=links.length; i<L; i++) { let random_item = links.pop() }
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Please consider explanation from comments. Array.prototype.splice()

var links = ["page-1", "page-2", "page-3", "page-108"]; // array to hold used link values which are removed form links. // when links is empty then assign all values back from linksUsed and clear linksUsed. var linksUsed = []; function openSite() { // if links is empty then assign all values back from linksUsed and clear linksUsed. if (links.length == 0) { links = linksUsed; linksUsed = []; } var randIdx = Math.random() * links.length; randIdx = parseInt(randIdx, 10); // splice will remove n items starting from index. // First parameter value is starting index and 2nd parameter is delete count var link = links.splice(randIdx, 1)[0]; // push removed link to linksUsed linksUsed.push(link); // update link link = 'https://websitename.com/page/' + link; // for testing commented below line and added log // window.location.assign(link); console.log(link); }; //for (let i = 0; i < 5; i++) { // openSite(); //}
<button onclick='openSite()'>Open Site</button>

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This code is working well in terms of preventing any repeats, but it's randomizing every few seconds. I want it to randomize on the click of a button. The button is programmed to do this, but with this Java code, that's not working. Any suggestions how I can make that work?
I guess what you need is call openSite function from button's onclick like <button onclick='openSite()'>. Also updated code, you can check it.
That's exactly why my HTML says but it's not working properly. Anything else that could assist that?
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<script> var links = ["page-1", "page-2", "page-3", ... "page-108", ] currentPage=1; function openSite() { var randIdx = Math.random() * links.length; randIdx = parseInt(randIdx, 10); console.log(currentPage) //this condition will detect repeat then increase randIdx by 1 if(randIdx==currentPage){ console.log('REPEATED') randIdx++ } // console.log(randIdx ) var link = 'https://websitename.com/page/' + links[randIdx]; window.location.assign(link); currentPage=randIdx; }; </script> 
<button onclick='openSite()'>CLICK</button>

This Simple condition will solve your repeating problem

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You can do this with Rando.js' randoSequence shuffle function and JavaSript's pop function like this:

var links = ["page-1", "page-2", "page-3", "page-4"], shuffledLinks = []; function getRandomLink() { return 'https://websitename.com/page/' + (shuffledLinks = shuffledLinks.length ? shuffledLinks : randoSequence(links)).pop().value; } for(var i = 0; i < 10; i++) console.log(getRandomLink());
<script src="https://randojs.com/2.0.0.js"></script>

This will create an array of shuffled links, remove from the shuffled array one at a time, and refill it as needed.

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