How to prevent repeating numbers in Math.random() javascript

Question

I have the following code (see below) in a HTML file that generates random numbers between the range 100000-999999 (It works fine) but I want to make sure it does not REPEAT itself. How do I modify it or add code to do that?

       
 
var randomnumber = Math.floor(Math.random()*999999) + 100000
document.write(randomnumber)

Do you want just prevent in same request or unique for other request? — ramin ashrafimanesh, Jan 24 '18 at 13:02
you might have a look here: https://stackoverflow.com/questions/40056297/random-number-which-is-not-equal-to-the-previous-number — Nina Scholz, Jan 24 '18 at 13:04

Faly · Answer 1 · 2018-01-24T13:07:49.943

3

You can keep track of all numbers that are already used:

var numbers = [];
var randomnumber;
do {
    randomnumber= Math.floor(Math.random()*999999) + 100000;
} while (numbers.includes(randomnumber));
numbers.push(randomnumber);     
document.write(randomnumber)

If ES6 is a problem (array.prototype.includes), you can use array.prototype.indexOf :

// ...
do {
    randomnumber= Math.floor(Math.random()*999999) + 100000;
} while (numbers.indexOf(randomnumber) !== -1);
// ...

edited Jan 24 '18 at 13:07

answered Jan 24 '18 at 13:03

Faly

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you were too fast :D nice solution – messerbill Jan 24 '18 at 13:03
A better solution would be to use `numbers.indexOf(randomnumber) !== -1` since that doesn't require the runtime to implement ES 2016. – Aurelia Jan 24 '18 at 13:05

How to prevent repeating numbers in Math.random() javascript

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