[rahul05ranjan]

What

The JSDoc for the standard option advertises "SI, IEC, JEDEC", but the STANDARD_CONFIGS lookup is keyed on the lowercase "si" / "iec" / "jedec", so an uppercase spelling misses the lookup and silently falls through to the decimal default — the wrong unit system:

filesize(1048576, { standard: "iec" }); // "1 MiB"
filesize(1048576, { standard: "IEC" }); // "1.05 MB"  <- decimal fallback, no warning
filesize(1000, { standard: "SI" });     // "1.00 kB"  <- happens to look right, by accident

Fix

Case-normalize the value in getBaseConfiguration() before the cached lookup. Unknown values keep the existing fallback behavior, which is pinned by the should fall back to JEDEC default for unknown standard test, so this change only affects spellings that are case variants of the three real standards — exactly the ones the JSDoc shows. The same normalization covers partial({ standard: "IEC" }).

Verification

• New tests in tests/unit/filesize.test.js (uppercase IEC/JEDEC/SI, the partial() path, and a guard that the unknown-value fallback is unchanged): 3 fail on main@d2bb4c1, all pass with this change.
• Full suite with the fix: node --test tests/unit/ — 278 pass, 0 fail (273 pre-existing + 5 new).