PHP's bcround in JavaScript

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

module.exports = function bcround (val, precision) {
// discuss at:
// original by: lmeyrick (
// example 1: bcround(1, 2)
// returns 1: '1.00'
const _bc = require('../_helpers/_bc')
const libbcmath = _bc()
let temp, result, digit
let rightOperand
// create number
temp = libbcmath.bc_init_num()
temp = libbcmath.php_str2num(val.toString())
// check if any rounding needs
if (precision >= temp.n_scale) {
// nothing to round, just add the zeros.
while (temp.n_scale < precision) {
temp.n_value[temp.n_len + temp.n_scale] = 0
return temp.toString()
// get the digit we are checking (1 after the precision)
// loop through digits after the precision marker
digit = temp.n_value[temp.n_len + precision]
rightOperand = libbcmath.bc_init_num()
rightOperand = libbcmath.bc_new_num(1, precision)
if (digit >= 5) {
// round away from zero by adding 1 (or -1) at the "precision"..
// ie 1.44999 @ 3dp = (1.44999 + 0.001).toString().substr(0,5)
rightOperand.n_value[rightOperand.n_len + rightOperand.n_scale - 1] = 1
if (temp.n_sign === libbcmath.MINUS) {
// round down
rightOperand.n_sign = libbcmath.MINUS
result = libbcmath.bc_add(temp, rightOperand, precision)
} else {
// leave-as-is.. just truncate it.
result = temp
if (result.n_scale > precision) {
result.n_scale = precision
return result.toString()
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How to use

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

If you intend to target the browser, you can then use a module bundler such as Parcel, webpack, Browserify, or rollup.js. This can be important because Locutus allows modern JavaScript in the source files, meaning it may not work in all browsers without a build/transpile step. Locutus does transpile all functions 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.


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
1bcround(1, 2)'1.00'

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