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Decimal step on NumberInputWidget results in cumulative binary rounding error
Open, LowPublic


Steps to reproduce:

  1. Go to, scroll down to "NumberInputWidget (0–1, step by .1, page by .25)"
  2. Enter "1".
  3. Press the down arrow key 10 times.

Expected: You end with 0.
Actual (Firefox): You reach 0.0000000000000001
Actual (Vivaldi): Rounding errors show up even before you should reach 0.

Event Timeline

Esanders created this task.Jun 11 2015, 3:15 PM
Esanders raised the priority of this task from to Needs Triage.
Esanders updated the task description. (Show Details)
Esanders added a project: OOUI.
Esanders added subscribers: Aklapper, Esanders.
Jdforrester-WMF triaged this task as Low priority.Mar 22 2016, 6:39 PM
Jdforrester-WMF set Security to None.
Esanders added a comment.EditedAug 2 2017, 10:48 AM

We should remove the decimal example from the demo, and document that step should be an integer to avoid floating point errors.

If someone comes up with a real-world need for decimal increments they should probably just extend the class and use a mapping function to generate non-integer steps (e.g. f(x) -> x/10) ) - if it's useful we can upstream it.

Short of pulling in a decimal type library we're not going to be able to mimic non-integer steps in JS and that seems overkill for a rarely used feature.

Esanders added a comment.EditedAug 2 2017, 11:00 AM

...or you could call stepUp()/stepDown() to exploit the native browser functionality, but support is sketchy?

Volker_E moved this task from Backlog to Next-up on the OOUI board.Feb 2 2018, 2:50 AM
Gustmd7410 removed a subscriber: Gustmd7410.