josdejong/mathjs

Avoid unnecessary parentheses for Units with complex value when using `format`

Open

#3614 opened on Dec 17, 2025

View on GitHub
 (4 comments) (0 reactions) (0 assignees)JavaScript (13,832 stars) (1,298 forks)batch import
category:unitsfeaturehelp wanted

Description

Describe the bug Some units are considered complex units, meaning they are treated differently to normal, "numeric" units. This for example is the case for the volt-ampere reactive, considered to be VAR by mathjs.

To Reproduce I am unsure why, but converting these units leads to unexpected results:

(new Unit(1, 'MW')).to('kW').format() // 1000 kW - correct
(new Unit(1, 'MVAR')).to('kVAR').format() // (1000) kVAR - weird
(new Unit(1, 'MVAR')).to('kW').format() // (1000i) kW - weird

I understand the want to represent these as complex numbers, but I think this is fairly out of place when dealing with units. It leads to unexpected conversions and format outputs.

Notice that using formatUnits avoids this, of course, since only the number part is affected by this:

(new Unit(1, 'MVAR')).to('kVAR').formatUnits() // kVAR
(new Unit(1, 'MVAR')).to('kW').formatUnits() // kW

Contributor guide

Tech stack
javascript
Domain
api
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScriptmathjs unit systembasic understanding of complex numbers
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
The bug is in the `Unit.format()` method, likely located in `src/type/unit/Unit.js`. Focus on how 'complex units' like VAR are detected and how parentheses are added to the numeric value during formatting. Look for the logic that applies complex number formatting and decide whether parentheses should be omitted when converting units. Check existing tests in `test/unit/Unit.test.js` for related test cases to understand expected behavior and ensure the fix doesn't break other unit formats.