Compose conditional class names

Loading problem workspace…

Compose conditional class names · UIHero

Compose conditional class names

Flatten strings, nested arrays, and conditional object flags into one stable class string.

EasyJavaScript Utilities

25 min0% acceptance

Description

Implement classNames as an immutable utility. It ignores falsy values, recursively flattens arrays, includes truthy object keys, and preserves the left-to-right encounter order of every resulting class token.

Requirements

The solution exports the required classNames API from the editable module.
Ignores falsy works deterministically for the documented normal, boundary, and repeated-use scenarios.
Nested arrays works deterministically for the documented normal, boundary, and repeated-use scenarios.
Object flags works deterministically for the documented normal, boundary, and repeated-use scenarios.
Preserves order works deterministically for the documented normal, boundary, and repeated-use scenarios.
Empty input works deterministically for the documented normal, boundary, and repeated-use scenarios.
Caller-owned inputs and nested values remain unchanged after the operation completes.

Mixed values

Input

classNames('button', ['large', null], { active: true, busy: false })

Expected output

button large active

Explanation

Falsy entries and false object flags are omitted while token order is retained.

Constraints

Support strings, arbitrarily nested arrays, objects, and falsy values
Do not mutate arrays or objects
Separate included tokens with one space

Hints

Hint 1

Use one recursive visitor that appends tokens to a shared output array.

Hint 2

Arrays recurse in order; objects contribute their keys when the corresponding value is truthy.

Hint 3

Filter at traversal time so the final operation is a simple join.

JavaScriptrecursionstrings

Loading problem workspace…