fix[orderBy, sortBy]: keep sort order consistent when values contain NaN

[minseonkkim]

Summary

When the sort key contains NaN, orderBy and sortBy leave the array partially unsorted.

import { sortBy } from 'es-toolkit';

const items = [{ v: 3 }, { v: NaN }, { v: 1 }, { v: 2 }, { v: 0 }];

sortBy(items, ['v']).map(item => item.v);
// Expected: [0, 1, 2, 3, NaN]
// Actual:   [3, NaN, 0, 1, 2]

compareAscending in src/_internal/compareValues.ts compares regular values with < and >. Every comparison involving NaN returns false, so NaN is treated as equal to every value. This breaks the transitivity the comparator relies on (3 == NaN, NaN == 0, but 3 > 0), and the sort produces an inconsistent result. Elements before the NaN are not sorted at all.

This can easily happen in practice, for example when a numeric field comes from a failed parseFloat or a 0 / 0 calculation.

I found this while reading the code, so there is no related issue.

Changes

• src/_internal/compareValues.ts: give NaN its own rank, so it never reaches the < / > comparison. The order is now regular values < NaN < null < undefined, following the existing approach for null and undefined.
• src/array/orderBy.spec.ts: add tests for ascending, descending, and mixed NaN / null / undefined cases.

The new tests fail on main and pass with this change.

I placed NaN before null and undefined because NaN is still a number, while null and undefined mean the value is missing. Lodash uses a different order (null < undefined < NaN), so I'm happy to change it if you prefer that.

es-toolkit/compat has its own compareValues, so it is not affected.

Benchmark results

main

 BENCH  Summary

   benchmarks  es-toolkit/orderBy - orderBy.bench.ts > orderBy
    1.77x faster than es-toolkit/compat/orderBy
    1.85x faster than lodash/orderBy

   benchmarks  es-toolkit/compat/orderBy - orderBy.bench.ts > orderBy (nested property names)
    1.41x faster than lodash/orderBy

   benchmarks  es-toolkit/compat/orderBy - orderBy.bench.ts > orderBy (property path)
    1.23x faster than lodash/orderBy

   benchmarks  es-toolkit/sortBy - sortBy.bench.ts > sortBy
    1.62x faster than es-toolkit/compat/sortBy
    1.74x faster than lodash/sortBy

   benchmarks  es-toolkit/compat/sortBy - sortBy.bench.ts > sortBy (nested property names)
    1.47x faster than lodash/sortBy

   benchmarks  es-toolkit/compat/sortBy - sortBy.bench.ts > sortBy (property path)
    1.13x faster than lodash/sortBy

This branch

 BENCH  Summary

   benchmarks  es-toolkit/orderBy - orderBy.bench.ts > orderBy
    2.07x faster than es-toolkit/compat/orderBy
    2.10x faster than lodash/orderBy

   benchmarks  es-toolkit/compat/orderBy - orderBy.bench.ts > orderBy (nested property names)
    1.39x faster than lodash/orderBy

   benchmarks  es-toolkit/compat/orderBy - orderBy.bench.ts > orderBy (property path)
    1.33x faster than lodash/orderBy

   benchmarks  es-toolkit/sortBy - sortBy.bench.ts > sortBy
    1.67x faster than es-toolkit/compat/sortBy
    1.84x faster than lodash/sortBy

   benchmarks  lodash/sortBy - sortBy.bench.ts > sortBy (nested property names)
    1.14x faster than es-toolkit/compat/sortBy

   benchmarks  es-toolkit/compat/sortBy - sortBy.bench.ts > sortBy (property path)
    1.19x faster than lodash/sortBy

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Project	Deployment	Actions	Updated
es-toolkit	Error		Oct 4, 2026 6:49am UTC