[chatman-media]

Summary

es-toolkit/compat aims for 100% behavioral parity with lodash, but round, ceil, and floor diverge when called on Infinity / -Infinity together with a non-zero precision: they return NaN instead of the infinite value.

import { round, ceil, floor } from 'es-toolkit/compat';

round(Infinity, 2);   // => NaN  (lodash: Infinity)
ceil(-Infinity, 2);   // => NaN  (lodash: -Infinity)
floor(Infinity, -2);  // => NaN  (lodash: Infinity)

// precision 0 / omitted already worked correctly:
round(Infinity);      // => Infinity ✓

Root cause

All three functions delegate to the internal decimalAdjust helper. When precision is non-zero it shifts the value using exponential string notation:

const [magnitude, exponent = 0] = number.toString().split('e');
let adjustedValue = Math[type](Number(`${magnitude}e${Number(exponent) + precision}`));

For Infinity, number.toString() is "Infinity", so the constructed string becomes "Infinitye2", which is not a valid number — Number("Infinitye2") is NaN. The precision === 0 path was unaffected because it skips this branch and calls Math[type](number) directly.

lodash guards this exact case in createRound by additionally checking that the number is finite before doing the exponential shift (lodash.js#L5481):

if (precision && nativeIsFinite(number)) { ... }

Fix

Mirror lodash by only applying the exponential-shift logic when the value is finite; otherwise fall through to Math[type](number), which returns the infinity unchanged.

-  if (precision) {
+  if (precision && Number.isFinite(Number(number))) {

The -0 handling is preserved (number may be the string '-0' at this point; Number('-0') is -0, which is finite), and NaN input still yields NaN via the fall-through, matching lodash.

Verification

• Added should return Infinity for infinite values regardless of precision tests to round, ceil, and floor spec files. They fail on main (NaN) and pass with this fix.
• Verified the new behavior matches lodash 4.17.21 across positive, negative, zero, and out-of-range precisions for both Infinity and -Infinity.
• Full es-toolkit/compat test suite passes (3091 tests); a fuzz comparison of the string/number compat functions against lodash now reports zero discrepancies.
• prettier and eslint clean on the changed files.

decimalAdjust is used only by round/ceil/floor, so the change is fully scoped to these three functions.

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Project	Deployment	Actions	Updated (UTC)
es-toolkit	Ready	Preview, Comment	Jun 10, 2026 6:47pm

[raon0211]

Thanks for your help!