Allow promises to be passed through a channel.

lib/index.js

@@ -59,9 +59,14 @@ const Channel = function(length = 0) {
         index.push++;
       } else if (shift.cancelled) {
         index.shift++;
+      } else {
+        if (`reason` in push) {
+          shift.reject(push.reason);
         } else {
           lastValue = push.value;
           shift.resolve(lastValue);
+        }
+
         buffered = Math.max(0, buffered - 1);
         index.push++;
         index.shift++;
@@ -320,6 +325,13 @@ const Channel = function(length = 0) {
         const { order, promise } = Order(this);
         order.value = value;
 
+        // If value is a promise that rejects, catch it in case there hasn't
+        // been a matching shift yet in order to prevent an unhandledRejection
+        // error.  Reject it again when there's a shift.
+        Promise.resolve(value).catch(reason => {
+          order.reason = reason;
+        });
+
         if (closed) {
           order.reject(new Error(`Can't push to closed channel.`));
         } else if (value === undefined) {

test/index.js

@@ -453,3 +453,25 @@ describe(`Channel object`, function() {
     });
   });
 });
+
+it(`allows promises to be sent through a channel`, function() {
+  return new Promise(async (resolve, reject) => {
+    process.once(`unhandledRejection`, reject);
+
+    const channel = Channel.of(
+      Promise.resolve(`resolved`),
+      new Promise((resolve, reject) => {
+        setImmediate(reject, new Error(`rejected`));
+      })
+    );
+
+    assert.equal(await channel.shift(), `resolved`);
+
+    try {
+      await channel.shift();
+    } catch (exception) {
+      assert.equal(exception.message, `rejected`);
+      resolve();
+    }
+  });
+});