PHP's round in JavaScript

How to use

You you can install via yarn add locutus and require this function via const round = require('locutus/php/math/round').

It is important to use a bundler that supports tree-shaking so that you only ship the functions that you actually use to your browser, instead of all of Locutus, which is massive. Examples are: Parcel, webpack, or rollup.js. For server-side use this is typically less of a concern.

Examples

Please note that these examples are distilled from test cases that automatically verify our functions still work correctly. This could explain some quirky ones.

#	code	expected result
1	round(1241757, -3)	1242000
2	round(3.6)	4
3	round(2.835, 2)	2.84
4	round(1.1749999999999, 2)	1.17
5	round(58551.799999999996, 2)	58551.8
6	round(4096.485, 2)	4096.49

Here’s what our current JavaScript equivalent to PHP's round looks like.

function roundToInt(value, mode) {
  let tmp = Math.floor(Math.abs(value) + 0.5)

  if (
    (mode === 'PHP_ROUND_HALF_DOWN' && value === tmp - 0.5) ||
    (mode === 'PHP_ROUND_HALF_EVEN' && value === 0.5 + 2 * Math.floor(tmp / 2)) ||
    (mode === 'PHP_ROUND_HALF_ODD' && value === 0.5 + 2 * Math.floor(tmp / 2) - 1)
  ) {
    tmp -= 1
  }

  return value < 0 ? -tmp : tmp
}

module.exports = function round(value, precision = 0, mode = 'PHP_ROUND_HALF_UP') {
  //  discuss at: https://locutus.io/php/round/
  // original by: Philip Peterson
  //  revised by: Onno Marsman (https://twitter.com/onnomarsman)
  //  revised by: T.Wild
  //  revised by: Rafał Kukawski (https://blog.kukawski.pl)
  //    input by: Greenseed
  //    input by: meo
  //    input by: William
  //    input by: Josep Sanz (https://www.ws3.es/)
  // bugfixed by: Brett Zamir (https://brett-zamir.me)
  //  revised by: Rafał Kukawski
  //   example 1: round(1241757, -3)
  //   returns 1: 1242000
  //   example 2: round(3.6)
  //   returns 2: 4
  //   example 3: round(2.835, 2)
  //   returns 3: 2.84
  //   example 4: round(1.1749999999999, 2)
  //   returns 4: 1.17
  //   example 5: round(58551.799999999996, 2)
  //   returns 5: 58551.8
  //   example 6: round(4096.485, 2)
  //   returns 6: 4096.49

  const floatCast = require('../_helpers/_php_cast_float')
  const intCast = require('../_helpers/_php_cast_int')
  let p

  // the code is heavily based on the native PHP implementation
  // https://github.com/php/php-src/blob/PHP-7.4/ext/standard/math.c#L355

  value = floatCast(value)
  precision = intCast(precision)
  p = Math.pow(10, precision)

  if (isNaN(value) || !isFinite(value)) {
    return value
  }

  // if value already integer and positive precision
  // then nothing to do, return early
  if (Math.trunc(value) === value && precision >= 0) {
    return value
  }

  // PHP does a pre-rounding before rounding to desired precision
  // https://wiki.php.net/rfc/rounding#pre-rounding_to_the_value_s_precision_if_possible
  const preRoundPrecision = 14 - Math.floor(Math.log10(Math.abs(value)))

  if (preRoundPrecision > precision && preRoundPrecision - 15 < precision) {
    value = roundToInt(value * Math.pow(10, preRoundPrecision), mode)
    value /= Math.pow(10, Math.abs(precision - preRoundPrecision))
  } else {
    value *= p
  }

  value = roundToInt(value, mode)

  return value / p
}

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we assimilate first iterations with imperfections, hoping for others to take issue with-and improve them. This unorthodox approach has worked very well to foster fun and fruitful collaboration, but please be reminded to use our creations at your own risk. THE SOFTWARE IS PROVIDED "AS IS" has never been more true than for Locutus.

Now go and: [ View on GitHub | Edit on GitHub | View Raw ]

---

« More PHP math functions

Star