4 files changed, 43 insertions, 0 deletions
diff --git a/js/globals.ts b/js/globals.ts
index e45aee9e2..9e7d20bcc 100644
--- a/js/globals.ts
+++ b/js/globals.ts
@@ -21,6 +21,7 @@ import * as timers from "./timers";
 import * as url from "./url";
 import * as urlSearchParams from "./url_search_params";
 import * as workers from "./workers";
+import * as performanceUtil from "./performance";
 
 // These imports are not exposed and therefore are fine to just import the
 // symbols required.
@@ -93,4 +94,6 @@ export type TextEncoder = textEncoding.TextEncoder;
 window.TextDecoder = textEncoding.TextDecoder;
 export type TextDecoder = textEncoding.TextDecoder;
 
+window.performance = new performanceUtil.Performance();
+
 window.workerMain = workers.workerMain;
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;
+  }
+}
diff --git a/js/performance_test.ts b/js/performance_test.ts
new file mode 100644
index 000000000..154dadbbe
--- /dev/null
+++ b/js/performance_test.ts
@@ -0,0 +1,10 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { test, assert } from "./test_util.ts";
+
+test(function now() {
+  const start = performance.now();
+  setTimeout(() => {
+    const end = performance.now();
+    assert(end - start >= 10);
+  }, 10);
+});
diff --git a/js/unit_tests.ts b/js/unit_tests.ts
index 418779f7f..edad57893 100644
--- a/js/unit_tests.ts
+++ b/js/unit_tests.ts
@@ -43,6 +43,7 @@ import "./truncate_test.ts";
 import "./url_test.ts";
 import "./url_search_params_test.ts";
 import "./write_file_test.ts";
+import "./performance_test.ts";
 
 import "../tools/util_test.ts";