random.js

import toFinite from './toFinite.js'

/** Built-in method references without a dependency on `root`. */
const freeParseFloat = parseFloat

/**
 * Produces a random number between the inclusive `lower` and `upper` bounds.
 * If only one argument is provided a number between `0` and the given number
 * is returned. If `floating` is `true`, or either `lower` or `upper` are
 * floats, a floating-point number is returned instead of an integer.
 *
 * **Note:** JavaScript follows the IEEE-754 standard for resolving
 * floating-point values which can produce unexpected results.
 *
 * @since 0.7.0
 * @category Number
 * @param {number} [lower=0] The lower bound.
 * @param {number} [upper=1] The upper bound.
 * @param {boolean} [floating] Specify returning a floating-point number.
 * @returns {number} Returns the random number.
 * @see uniqueId
 * @example
 *
 * random(0, 5)
 * // => an integer between 0 and 5
 *
 * random(5)
 * // => also an integer between 0 and 5
 *
 * random(5, true)
 * // => a floating-point number between 0 and 5
 *
 * random(1.2, 5.2)
 * // => a floating-point number between 1.2 and 5.2
 */
function random(lower, upper, floating) {
  if (floating === undefined) {
    if (typeof upper == 'boolean') {
      floating = upper
      upper = undefined
    }
    else if (typeof lower == 'boolean') {
      floating = lower
      lower = undefined
    }
  }
  if (lower === undefined && upper === undefined) {
    lower = 0
    upper = 1
  }
  else {
    lower = toFinite(lower)
    if (upper === undefined) {
      upper = lower
      lower = 0
    } else {
      upper = toFinite(upper)
    }
  }
  if (lower > upper) {
    const temp = lower
    lower = upper
    upper = temp
  }
  if (floating || lower % 1 || upper % 1) {
    const rand = Math.random()
    const randLength = `${ rand }`.length - 1
    return Math.min(lower + (rand * (upper - lower + freeParseFloat(`1e-${ randLength }`)), upper))
  }
  return lower + Math.floor(Math.random() * (upper - lower + 1))
}

export default random