Add performance.now (#1633)

1 files changed, 29 insertions, 0 deletions

diff --git a/js/performance.ts b/js/performance.ts
new file mode 100644
index 000000000..73378b15c
--- /dev/null
+++ b/js/performance.ts
@@ -0,0 +1,29 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import * as msg from "gen/msg_generated";
+import { sendSync } from "./dispatch";
+import * as flatbuffers from "./flatbuffers";
+import { assert } from "./util";
+
+export class Performance {
+  timeOrigin = 0;
+
+  constructor() {
+    this.timeOrigin = new Date().getTime();
+  }
+
+  /** Returns a current time from Deno's start
+   *
+   *       const t = performance.now();
+   *       console.log(`${t} ms since start!`);
+   */
+  now(): number {
+    const builder = flatbuffers.createBuilder();
+    msg.Now.startNow(builder);
+    const inner = msg.Now.endNow(builder);
+    const baseRes = sendSync(builder, msg.Any.Now, inner)!;
+    assert(msg.Any.NowRes === baseRes.innerType());
+    const res = new msg.NowRes();
+    assert(baseRes.inner(res) != null);
+    return res.time().toFloat64() - this.timeOrigin;
+  }
+}