Stop using node:perf_hooks (#1704)

.changeset/strong-cougars-push.md

@@ -0,0 +1,7 @@
+---
+"@siteimprove/alfa-performance": patch
+---
+
+**Changed:** `Performance.now()` does not try to use `node:perf_hooks` anymore.
+
+This created problem when trying to bundle `Performance` for browsers, where `node:` imports are not available.

packages/alfa-performance/src/now.ts

@@ -1,25 +1,22 @@
 /// <reference lib="dom" />
 
-import type { Thunk } from "@siteimprove/alfa-thunk";
-
-import perfHooks from "node:perf_hooks";
-
-export let now: Thunk<number>;
-
-/**
- * The continuations are needed to correctly handle the "this" bindings.
- * Eta-contracting breaks in node 19.0.0 and above. This may be linked to the
- * upgrade to V8 10.7.
+/*
+ * Performance measurement comes from different places in NodeJS and browser
+ * environments. The former uses node:perf_hooks, while the latter uses the
+ * global performance object. Trying to use the wrong one leads to at best
+ * undefined value, at worst compile errors at build time.
  *
- * Date.now actually works without the eta-expansion, keeping it for
- * consistency.
+ * It seems to not be that easy to polyfill between the two. While it is easy
+ * to test whether performance is defined, trying to import perf_hooks is enough
+ * to crash bundlers like Webpack.
+ *
+ * Therefore, we just ignore node:perf_hooks and defaults to the widely available
+ * Date.now() if the performance object is not available.
  */
-if (typeof performance !== "undefined") {
-  now = () => performance.now();
-} else {
-  try {
-    now = () => perfHooks.performance.now();
-  } catch {
-    now = () => Date.now();
-  }
-}
+
+import type { Thunk } from "@siteimprove/alfa-thunk";
+
+export const now: Thunk<number> =
+  typeof performance !== "undefined"
+    ? () => performance.now()
+    : () => Date.now();