How to create a random number generator function using JavaScript without using the Math.random() function?

Question

I want to create a random number generator function using JavaScript that will return a random number between 0 and 1. Is it possible to create a custom random number generator function without using the Math.random() function?

I tried this approach. It works but I don't know if it is really random or there is any pattern?

 var lastRand = 0.5; function rand(){ var x = new Date().getTime()*Math.PI*lastRand; var randNum = x%1; lastRand = randNum; return randNum; } // Output for(var n = 0; n < 50; n++){ console.log(rand()); }

This function depends on the variable lastRand to generate the number. But I want more efficient way to do it.

You should look into common techniques for pseudo-random number generation. — Pointy
– Pointy, Commented Mar 29, 2019 at 15:16
Repost! Go find your answer here: stackoverflow.com/questions/13442611/… — olajensola
– olajensola, Commented Mar 29, 2019 at 15:17
I found this wondergiant.com/2013/03/random-without-math-random , this might help you out — OlaJens
– OlaJens, Commented Mar 29, 2019 at 15:19

Nelson Teixeira · Accepted Answer · 2019-03-29 15:38:26Z

Why not this way ? It seems more random to me as it doesn't depend on a value.

var lastRand, randNum; function rand(){ while(randNum == lastRand) randNum = (new Date().getTime()*Math.PI)%1; return lastRand = randNum; } // Output for(var n = 0; n < 50; n++) console.log(rand());

Adnan Toky · Accepted Answer · 2019-03-31 14:32:56Z

I've got a better solution. It uses object instead of external variable.

var Random = { "lastRand" : 0.5, "randNum" : 0.5, "rand" : function(){ while(this.randNum == this.lastRand){ this.randNum = (new Date().getTime()*Math.PI*this.lastRand)%1; } return this.lastRand = this.randNum; } } for(var n = 0; n < 50; n++){ console.log(Random.rand()); }

Guilherme Amantea · Accepted Answer · 2019-03-29 16:15:06Z

This is a version using a function generator which doesn't require external variables.

function *makeRand() { let seed = new Date().getTime() while (true) { seed = seed * 16807 % 2147483647 yield seed / 2147483647 } } // Usage let rand = makeRand() for (let i = 0; i < 5; i++) { console.log(rand.next().value) } // 0.05930273982663767 // 0.7011482662992311 // 0.1989116911771296 // 0.10879361401721538 // 0.4942707873388523

Source: https://www.cse.wustl.edu/~jain/iucee/ftp/k_26rng.pdf

It's a good solution. But I've noticed a pattern in this method. If I reload the page after every 1 second, I find a pattern like this. 0.22..., 0.24...., 0.26...., 0.28... among the first number.
Maybe you’re calling makeRand() all the time? Make sure to store the resulting rand and use that to call next() multiple times.

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