Add an example of the performance API

examples/performance/src/lib.rs

@@ -0,0 +1,51 @@
+#![feature(proc_macro)]
+
+extern crate wasm_bindgen;
+extern crate humantime;
+
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+use wasm_bindgen::prelude::*;
+
+// Like with the `dom` example this block will eventually be auto-generated, but
+// for now we can write it by hand to get by!
+#[wasm_bindgen]
+extern {
+    type Performance;
+    static performance: Performance;
+    #[wasm_bindgen(method)]
+    fn now(this: &Performance) -> f64;
+    #[wasm_bindgen(method, getter)]
+    fn timing(this: &Performance) -> PerformanceTiming;
+
+    type PerformanceTiming;
+    #[wasm_bindgen(method, getter)]
+    fn requestStart(this: &PerformanceTiming) -> f64;
+    #[wasm_bindgen(method, getter)]
+    fn responseEnd(this: &PerformanceTiming) -> f64;
+
+    #[wasm_bindgen(namespace = console)]
+    fn log(a: &str);
+}
+
+macro_rules! println {
+    ($($t:tt)*) => (console::log(&format_args!($($t)*).to_string()))
+}
+
+// Called by our JS entry point to run the example
+#[wasm_bindgen]
+pub fn run() {
+    println!("the current time is {}", performance.now());
+
+    let start = perf_to_system(performance.timing().requestStart());
+    let end = perf_to_system(performance.timing().responseEnd());
+
+    println!("request started at {}", humantime::format_rfc3339(start));
+    println!("request ended at {}", humantime::format_rfc3339(end));
+}
+
+fn perf_to_system(amt: f64) -> SystemTime {
+    let secs = (amt as u64) / 1_000;
+    let nanos = ((amt as u32) % 1_000) * 1_000_000;
+    UNIX_EPOCH + Duration::new(secs, nanos)
+}