Add Instant

Cargo.toml

@@ -10,5 +10,6 @@ local-offset = [ "time/local-offset" ]
 time = "0.3"
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
-js-sys = "0.3.57"
+js-sys = { version = "0.3.57", default-features = false }
+web-sys = { version = "0.3.57", default-features = false, features = [ "Window", "Performance" ] }
 

src/lib.rs

@@ -1,3 +1,4 @@
+use time::Duration;
 use time::OffsetDateTime;
 
 #[cfg(target_arch = "wasm32")]
@@ -12,6 +13,45 @@ pub fn now_utc() -> OffsetDateTime {
     return OffsetDateTime::now_utc();
 }
 
+#[cfg(target_arch = "wasm32")]
+type InnerInstant = Duration;
+#[cfg(not(target_arch = "wasm32"))]
+type InnerInstant = time::Instant;
+
+/// On wasm32, represented as a [`Duration`] from an arbitrary epoch. On other architectures,
+/// represented as [`time::Instant`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[repr(transparent)]
+pub struct Instant(InnerInstant);
+
+impl Instant {
+    #[cfg(target_arch = "wasm32")]
+    pub fn now() -> Instant {
+        let stamp = web_sys::window().expect("cannot get window").performance().expect("cannot get performance").now();
+        return Instant(Duration::seconds_f64(stamp / 1_000f64));
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    #[inline(always)]
+    pub fn now() -> Instant {
+        return Instant(time::Instant::now());
+    }
+
+    #[inline(always)]
+    pub fn elapsed(self) -> Duration {
+        Self::now() - self
+    }
+}
+
+impl std::ops::Sub for Instant {
+    type Output = Duration;
+
+    #[inline(always)]
+    fn sub(self, rhs: Self) -> Self::Output {
+        self.0 - rhs.0
+    }
+}
+
 #[cfg(feature = "local-offset")]
 #[cfg(target_arch = "wasm32")]
 pub fn current_local_offset() -> Result<time::UtcOffset, time::error::IndeterminateOffset> {