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fix: do not round non-zero values down to zero #264

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fix: do not round non-zero values down to zero #264

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8 changes: 7 additions & 1 deletion src/lib/serialize.js
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,8 @@
* @property {string} [calcName] Wrapper name to use when `calc()` is needed. Default `'calc'`.
*/

const NOISE_FLOOR = 1e-12;

/**
* @param {number} v
* @param {number | false} prec
Expand All @@ -25,7 +27,11 @@ function round(v, prec) {
return v;
}
const m = Math.pow(10, prec);
return Math.round(v * m) / m;
const rounded = Math.round(v * m) / m;

@ludofischer ludofischer Jul 21, 2026

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Should be some comment about explaining why the code is doing this or nobody will understand it in the future.

if (rounded === 0 && Math.abs(v) > NOISE_FLOOR) {
return v < 0 ? -1 / m : 1 / m;
}
return rounded;
}

// §10.13 / §10.7.2: Infinity/NaN serialize as canonical keywords.
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20 changes: 20 additions & 0 deletions test/index.js
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Expand Up @@ -382,6 +382,26 @@ test(
testValue('calc(5/1000000)', '0.000005', { precision: 6 })
);

test(
'should not round a non-zero value down to zero',
testValue('calc(1/1000000)', '0.00001')

@ludofischer ludofischer Jul 21, 2026

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Why does dividing 1 by one million give 1e-06 instead of 1e-05? I guess it's related to the precision being 5 decimal digits, but I would appreciate some explanation or a link to the spec.

);

test(
'should not round a non-zero dimension down to zero',
testValue('calc(1px/1000000)', '0.00001px')
);

test(
'should not round a non-zero negative value down to zero',
testValue('calc(-1/1000000)', '-0.00001')
);

test(
'should keep rounding float noise to zero',
testValue('calc(0.1px + 0.2px - 0.3px)', '0px')
);

test(
'should reduce browser-prefixed calc (1)',
testValue('-webkit-calc(1px + 1px)', '2px')
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