Simplify implementation of select.

lib/index.js

@@ -403,45 +403,45 @@ Channel.of = (...values) => Channel.from(values);
 Channel.isChannel = arg =>
   arg !== undefined && arg !== null && Object.getPrototypeOf(arg) === prototype;
 
-Channel.select = methodPromises =>
-  Object.assign(
-    new Promise((resolve, reject) => {
+Channel.select = methodPromises => {
+  if (!Array.isArray(methodPromises)) {
+    throw new TypeError(`Channel.select: Argument must be an array.`);
+  }
+
+  const selectPromise = new Promise((resolve, reject) => {
+    methodPromises.forEach(async promise => {
       try {
-        methodPromises.forEach(async promise => {
-          try {
-            promise.prethen(() => {
-              // We've been given a heads-up that this method will complete first
-              // so cancel the other method calls.
-              methodPromises.forEach(other => {
-                if (other !== promise) {
-                  other.cancel();
-                }
-              });
-            });
-
-            try {
-              await promise;
-            } catch (exception) {
-              reject(exception);
+        promise.prethen(() => {
+          // We've been given a heads-up that this method will complete first
+          // so cancel the other method calls.
+          methodPromises.forEach(other => {
+            if (other !== promise) {
+              other.cancel();
             }
-
-            resolve(promise.channel);
-          } catch (exception) {
-            reject(
-              new TypeError(
-                `Channel.select accepts only promises returned by push & shift.`
-              )
-            );
-          }
+          });
         });
+
+        try {
+          await promise;
+        } catch (exception) {
+          reject(exception);
+        }
+
+        resolve(promise.channel);
       } catch (exception) {
-        reject(new TypeError(`Channel.select: Argument must be an array.`));
+        reject(
+          new TypeError(
+            `Channel.select accepts only promises returned by push & shift.`
+          )
+        );
       }
-    }),
-    {
-      cancel: () => Promise.all(methodPromises.map(promise => promise.cancel()))
-    }
-  );
+    });
+  });
+
+  return Object.assign(selectPromise, {
+    cancel: () => methodPromises.forEach(promise => promise.cancel())
+  });
+};
 
 // functional interface allowing full or partial application
 //

test/index.js

@@ -98,6 +98,7 @@ describe(`Channel function`, function() {
     it(`miscellaneous`, async function() {
       const a = Channel();
       const b = Channel();
+
       (async () => {
         await b.push(0);
         await a.push(1);
@@ -114,10 +115,9 @@ describe(`Channel function`, function() {
   it(`allows for non-blocking selects`, async function() {
     const a = Channel();
     const b = Channel();
+    const closed = Channel.of();
 
-    switch (
-      await Channel.select([a.shift(), b.push(0), Channel.of().shift()])
-    ) {
+    switch (await Channel.select([a.shift(), b.push(0), closed.shift()])) {
       case a:
         assert(false);
         break;