Implement Debug for JsFuture

crates/futures/src/lib.rs

@@ -104,6 +104,7 @@
 #![deny(missing_docs)]
 
 use std::cell::{Cell, RefCell};
+use std::fmt;
 use std::rc::Rc;
 use std::sync::Arc;
 
@@ -128,6 +129,12 @@ pub struct JsFuture {
     callbacks: Option<(Closure<FnMut(JsValue)>, Closure<FnMut(JsValue)>)>,
 }
 
+impl fmt::Debug for JsFuture {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "JsFuture {{ ... }}")
+    }
+}
+
 impl From<Promise> for JsFuture {
     fn from(js: Promise) -> JsFuture {
         // Use the `then` method to schedule two callbacks, one for the

crates/futures/tests/tests.rs

@@ -52,6 +52,13 @@ fn error_future_is_rejected_promise() -> impl Future<Item = (), Error = JsValue>
     })
 }
 
+#[wasm_bindgen_test]
+fn debug_jsfuture() {
+    let p = js_sys::Promise::resolve(&JsValue::from(42));
+    let f = JsFuture::from(p);
+    assert_eq!(&format!("{:?}", f), "JsFuture { ... }");
+}
+
 #[wasm_bindgen]
 extern "C" {
     fn setTimeout(c: &Closure<FnMut()>);