`startsWith` is 3.9× faster than a `/^s1/` regex

For a plain prefix check, startsWith beats a regular expression. Hoisting the regex literal out of the loop still leaves a 3.9× gap.

Result

Run	`/^s1/` regex	`String.startsWith`	Ratio
Run 1	3.821	0.944	4.05×
Run 2	3.325	0.862	3.86×
Run 3	3.075	0.836	3.68×

Median spread: `/^s1/` regex CV 9.1% / `String.startsWith` CV 5.2% / Ratio CV 3.9% (computed from the 3 runs)

Conditions

One prefix test per string, across 100,000 strings.

Where this number does not apply

Once the pattern gets complex — several alternatives, suffix matches, boundary rules — the regex becomes the better tool.

Reproduce

cd bench
node --expose-gc micro-fixed.mjs --out ../data/run.json --samples 21

Run it three times on the same machine; if the spread of median stays under 10%, you should land on the same conclusion. If your numbers disagree, tell us and we will retract.