tools(bench): rebootstrap (#12281)

Enable deno devs to bench/profile/test JS code changes without doing a full --release rebuild.

Incremental release builds take ~4mn on M1s, often more on other machines ...

1 files changed, 25 insertions, 0 deletions

diff --git a/tools/bench/rebench.js b/tools/bench/rebench.js
new file mode 100644
index 000000000..bbc5a3c2f
--- /dev/null
+++ b/tools/bench/rebench.js
@@ -0,0 +1,25 @@
+export function benchSync(name, n, innerLoop) {
+  const t1 = Date.now();
+  for (let i = 0; i < n; i++) {
+    innerLoop(i);
+  }
+  const t2 = Date.now();
+  console.log(benchStats(name, n, t1, t2));
+}
+
+export async function benchAsync(name, n, innerLoop) {
+  const t1 = Date.now();
+  for (let i = 0; i < n; i++) {
+    await innerLoop(i);
+  }
+  const t2 = Date.now();
+  console.log(benchStats(name, n, t1, t2));
+}
+
+function benchStats(name, n, t1, t2) {
+  const dt = (t2 - t1) / 1e3;
+  const r = n / dt;
+  const ns = Math.floor(dt / n * 1e9);
+  return `${name}:${" ".repeat(20 - name.length)}\t` +
+    `n = ${n}, dt = ${dt.toFixed(3)}s, r = ${r.toFixed(0)}/s, t = ${ns}ns/op`;
+}