Merge pull request #649 from share/next-tick-check

♻️ Check `nextTick` polyfill once at module level

lib/next-tick.js

@@ -0,0 +1,26 @@
+exports.messageChannel = function() {
+  var triggerCallback = createNextTickTrigger(arguments);
+  var channel = new MessageChannel();
+  channel.port1.onmessage = function() {
+    triggerCallback();
+    channel.port1.close();
+  };
+  channel.port2.postMessage('');
+};
+
+exports.setTimeout = function() {
+  var triggerCallback = createNextTickTrigger(arguments);
+  setTimeout(triggerCallback);
+};
+
+function createNextTickTrigger(args) {
+  var callback = args[0];
+  var _args = [];
+  for (var i = 1; i < args.length; i++) {
+    _args[i - 1] = args[i];
+  }
+
+  return function triggerCallback() {
+    callback.apply(null, _args);
+  };
+}

lib/util.js

@@ -1,3 +1,4 @@
+var nextTickImpl = require('./next-tick');
 
 exports.doNothing = doNothing;
 function doNothing() {}
@@ -85,31 +86,13 @@ exports.truthy = function(arg) {
   return !!arg;
 };
 
-exports.nextTick = function(callback) {
-  if (typeof process !== 'undefined' && process.nextTick) {
-    return process.nextTick.apply(null, arguments);
-  }
-
-  var args = [];
-  for (var i = 1; i < arguments.length; i++) {
-    args[i - 1] = arguments[i];
-  }
-
-  if (typeof MessageChannel === 'undefined') {
-    return setTimeout(triggerCallback);
-  }
-
-  var channel = new MessageChannel();
-  channel.port1.onmessage = function() {
-    triggerCallback();
-    channel.port1.close();
-  };
-  channel.port2.postMessage('');
-
-  function triggerCallback() {
-    callback.apply(null, args);
-  }
-};
+if (typeof process !== 'undefined' && typeof process.nextTick === 'function') {
+  exports.nextTick = process.nextTick;
+} else if (typeof MessageChannel !== 'undefined') {
+  exports.nextTick = nextTickImpl.messageChannel;
+} else {
+  exports.nextTick = nextTickImpl.setTimeout;
+}
 
 exports.clone = function(obj) {
   return (obj === undefined) ? undefined : JSON.parse(JSON.stringify(obj));

test/next-tick.js

@@ -0,0 +1,26 @@
+var nextTickImpl = require('../lib/next-tick');
+var expect = require('chai').expect;
+
+describe('nextTick', function() {
+  ['messageChannel', 'setTimeout'].forEach(function(name) {
+    var tick = nextTickImpl[name];
+
+    it('passes args', function(done) {
+      tick(function(arg1, arg2, arg3) {
+        expect(arg1).to.equal('foo');
+        expect(arg2).to.equal(123);
+        expect(arg3).to.be.undefined;
+        done();
+      }, 'foo', 123);
+    });
+
+    it('calls asynchronously', function(done) {
+      var called = false;
+      tick(function() {
+        called = true;
+        done();
+      });
+      expect(called).to.be.false;
+    });
+  });
+});