Rands.js provides methods to generate pseudorandom numbers from various distributions (e.g., uniform, Gaussian, Poisson, binomial, etc.). Rands.js can be used in conjunction with a seeded random number generator (RNG) to produce repeatable sequences of random values.

npm install rands

In your code:

var Rands = require('rands');
var r = new Rands();

While a tool like Webpack or Browserify is recommended for use in the browser, the rands.min.js script is also provided, which exposes the window.Rands global variable:

<script src="path/to/rands.min.js"></script>
<script>
  var r = new Rands();
  ...
</script>

The library provides methods to generate values from the following distributions.

In each case, the final argument length is optional. When included, the function returns an array of random variables of length length. When omitted, the function returns a single numeric value.

Generate Bernoulli random variable(s) with parameter p:

r.bernoulli(p, [length])

Generate binomial random variable(s) given n trials and p probability of success in each trial:

r.binomial(n, p, [length])

Generate exponential random variable(s) with rate parameter lambda:

r.exponential(lambda, [length])

Generate uniformly distributed integer(s) in range [min, max):

r.integer(min, max, [length])

Generate normally distributed random variable(s) with mean mean and standard deviation stdev, where mean=0 and stdev=1 by default:

r.normal([mean], [stdev], [length])

Generate Poisson random variable(s) with parameter lambda:

r.poisson(lambda, [length])

Generate Rayleigh random variable(s) with scale parameter sigma:

r.rayleigh(sigma, [length])

Generate uniform random variable(s) in range [min, max), where min=0 and max=1 by default:

r.uniform([min], [max], [length])

A few static methods are provided:

Compute the mean of the numbers contained in in array a:

Rands.mean(a)

Compute the variance of the numbers contained in array a:

Rands.variance(a)

The Rands([rngFunc]) constructor accepts a uniform random number generator function as an optional argument. By providing a seeded RNG function, your code can generate the same sequence of pseudorandom numbers every time it runs.

This is demonstrated in following example using David Bau's seedrandom.js package. The script will print the same number to the console every time it runs:

var Rands = require('rands');
var seedrandom = require('seedrandom');

var rngFunc = seedrandom('charlotte');
var r = new Rands(rngFunc);

console.log(r.uniform());

When an RNG function is not passed to the Rands constructor, the library will fall back to the built-in Math.random() function.