fix: improve v4() performance (#894)

Author: broofa

src/v4.ts

@@ -3,21 +3,11 @@ import rng from './rng.js';
 import { unsafeStringify } from './stringify.js';
 import { UUIDTypes, Version4Options } from './types.js';
 
-function v4(options?: Version4Options, buf?: undefined, offset?: number): string;
-function v4<TBuf extends Uint8Array = Uint8Array>(
-  options: Version4Options | undefined,
-  buf: TBuf,
-  offset?: number
-): TBuf;
-function v4<TBuf extends Uint8Array = Uint8Array>(
+function _v4<TBuf extends Uint8Array = Uint8Array>(
   options?: Version4Options,
   buf?: TBuf,
   offset?: number
 ): UUIDTypes<TBuf> {
-  if (native.randomUUID && !buf && !options) {
-    return native.randomUUID();
-  }
-
   options = options || {};
 
   const rnds = options.random ?? options.rng?.() ?? rng();
@@ -46,4 +36,26 @@ function v4<TBuf extends Uint8Array = Uint8Array>(
   return unsafeStringify(rnds);
 }
 
+function v4(options?: Version4Options, buf?: undefined, offset?: number): string;
+function v4<TBuf extends Uint8Array = Uint8Array>(
+  options: Version4Options | undefined,
+  buf: TBuf,
+  offset?: number
+): TBuf;
+function v4<TBuf extends Uint8Array = Uint8Array>(
+  options?: Version4Options,
+  buf?: TBuf,
+  offset?: number
+): UUIDTypes<TBuf> {
+  if (native.randomUUID && !buf && !options) {
+    return native.randomUUID();
+  }
+
+  // Putting tail-code that could just go inline here in a separate function
+  // allows for compiler optimizations that dramatically improve performance.
+  //
+  // REF: https://github.com/uuidjs/uuid/issues/892
+  return _v4(options, buf, offset);
+}
+
 export default v4;