perf(sdk-trace-base): use Uint8Array for browser RandomIdGenerator

CHANGELOG.md

@@ -29,6 +29,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 * refactor(sdk-metrics): simplify AllowList and DenyList processors [#6159](https://github.com/open-telemetry/opentelemetry-js/pull/6159) @cjihrig
 * chore: disallow constructor parameter property syntax [#6187](https://github.com/open-telemetry/opentelemetry-js/pull/6187) @legendecas
 * refactor(sdk-metrics): use test() instead of match() in isValidName() [#6205](https://github.com/open-telemetry/opentelemetry-js/pull/6205) @cjihrig
+* perf(sdk-trace-base): use Uint8Array for browser RandomIdGenerator [#6209](https://github.com/open-telemetry/opentelemetry-js/pull/6209) @overbalance
 
 ## 2.2.0
 

packages/opentelemetry-sdk-trace-base/src/platform/browser/RandomIdGenerator.ts

@@ -16,36 +16,56 @@
 
 import { IdGenerator } from '../../IdGenerator';
 
-const SPAN_ID_BYTES = 8;
 const TRACE_ID_BYTES = 16;
+const SPAN_ID_BYTES = 8;
+
+const TRACE_BUFFER = new Uint8Array(TRACE_ID_BYTES);
+const SPAN_BUFFER = new Uint8Array(SPAN_ID_BYTES);
+
+// Byte-to-hex lookup is faster than toString(16) in browsers
+const HEX: string[] = Array.from({ length: 256 }, (_, i) =>
+  i.toString(16).padStart(2, '0')
+);
+
+/**
+ * Fills buffer with random bytes, ensuring at least one is non-zero
+ * per W3C Trace Context spec.
+ */
+function randomFill(buf: Uint8Array): void {
+  for (let i = 0; i < buf.length; i++) {
+    buf[i] = (Math.random() * 256) >>> 0;
+  }
+  // Ensure non-zero
+  for (let i = 0; i < buf.length; i++) {
+    if (buf[i] > 0) return;
+  }
+  buf[buf.length - 1] = 1;
+}
+
+function toHex(buf: Uint8Array): string {
+  let hex = '';
+  for (let i = 0; i < buf.length; i++) {
+    hex += HEX[buf[i]];
+  }
+  return hex;
+}
 
 export class RandomIdGenerator implements IdGenerator {
   /**
    * Returns a random 16-byte trace ID formatted/encoded as a 32 lowercase hex
    * characters corresponding to 128 bits.
    */
-  generateTraceId = getIdGenerator(TRACE_ID_BYTES);
+  generateTraceId(): string {
+    randomFill(TRACE_BUFFER);
+    return toHex(TRACE_BUFFER);
+  }
 
   /**
    * Returns a random 8-byte span ID formatted/encoded as a 16 lowercase hex
    * characters corresponding to 64 bits.
    */
-  generateSpanId = getIdGenerator(SPAN_ID_BYTES);
-}
-
-const SHARED_CHAR_CODES_ARRAY = Array(32);
-function getIdGenerator(bytes: number): () => string {
-  return function generateId() {
-    for (let i = 0; i < bytes * 2; i++) {
-      SHARED_CHAR_CODES_ARRAY[i] = Math.floor(Math.random() * 16) + 48;
-      // valid hex characters in the range 48-57 and 97-102
-      if (SHARED_CHAR_CODES_ARRAY[i] >= 58) {
-        SHARED_CHAR_CODES_ARRAY[i] += 39;
-      }
-    }
-    return String.fromCharCode.apply(
-      null,
-      SHARED_CHAR_CODES_ARRAY.slice(0, bytes * 2)
-    );
-  };
+  generateSpanId(): string {
+    randomFill(SPAN_BUFFER);
+    return toHex(SPAN_BUFFER);
+  }
 }