PHP's round in JavaScript

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

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function roundToInt (value, mode) {
var 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

var floatCast = require('../_helpers/_php_cast_float')
var intCast = require('../_helpers/_php_cast_int')
var 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
var 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
}
[ View on GitHub | Edit on GitHub | Source on GitHub ]

How to use

You you can install via npm install locutus and require it via require('locutus/php/math/round'). You could also require the math module in full so that you could access math.round instead.

If you intend to target the browser, you can then use a module bundler such as Browserify, webpack or rollup.js.

ES5/ES6

This function targets ES5, but as of Locutus 2.0.2 we also support ES6 functions. Locutus transpiles to ES5 before publishing to npm.

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we don't consider it to be a bad thing that many of our functions are first iterations, which may still have their fair share of issues. We hope that these flaws will inspire others to come up with better ideas.

This way of working also means that we don't offer any production guarantees, and recommend to use Locutus inspiration and learning purposes only.

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.

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

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