lib0/random.js

/**
 * Isomorphic module for true random numbers / buffers / uuids.
 *
 * Attention: falls back to Math.random if the browser does not support crypto.
 *
 * @module random
 */

import * as math from './math.js'
import * as binary from './binary.js'
import { cryptoRandomBuffer } from './isomorphic.js'

export const rand = Math.random

export const uint32 = () => new Uint32Array(cryptoRandomBuffer(4))[0]

export const uint53 = () => {
  const arr = new Uint32Array(cryptoRandomBuffer(8))
  return (arr[0] & binary.BITS21) * (binary.BITS32 + 1) + (arr[1] >>> 0)
}

/**
 * @template T
 * @param {Array<T>} arr
 * @return {T}
 */
export const oneOf = arr => arr[math.floor(rand() * arr.length)]

// @ts-ignore
const uuidv4Template = [1e7] + -1e3 + -4e3 + -8e3 + -1e11
export const uuidv4 = () => uuidv4Template.replace(/[018]/g, /** @param {number} c */ c =>
  (c ^ uint32() & 15 >> c / 4).toString(16)
)