Add waterfall flow

async-lite.js

@@ -175,8 +175,28 @@
       }
 
       runTask(0);
-    }
+    },
 
+    // https://github.com/rzr/async-waterfall
+    waterfall : function waterfall(tasks, callback /* ... */) {
+      var results = Array.prototype.slice.call(arguments, 2);
+      if (!tasks.length) {
+        results.splice(0, 0, null);  // insert "err" before "results"
+        callback.apply(null, results);
+      } else {
+        var funct = tasks.shift();
+        results.push(function(err,res) {
+          if (err) {
+              return callback(err,res);
+          }
+          var args = [tasks, callback];
+          Array.prototype.push.apply(
+            args, Array.prototype.slice.call(arguments, 1));
+          waterfall.apply(null, args);
+        });
+        funct.apply(null, results);
+      }
+    }
   };
 
   // Node.js

test/waterfall.js

@@ -0,0 +1,135 @@
+var async = require('../async-lite.js');
+var expect = require('expect.js');
+
+describe('async.waterfall', function() {
+
+  it('should only process task arrays with at least 1 task', function(done) {
+
+    async.waterfall([], function(err, results) {
+
+      expect(err).to.not.be.ok();
+      expect(results).to.not.be.ok();
+      done();
+
+    });
+
+  });
+
+  it('should only process 1 task in the array at a time', function(done) {
+
+    var start_time = Date.now();
+
+    async.series([
+
+      function task1(callback) {
+        setTimeout(function() {
+          callback();
+        }, 200);
+      },
+
+      function task2(callback) {
+        setTimeout(function() {
+          callback();
+        }, 400);
+      },
+
+      function task3(callback) {
+        setTimeout(function() {
+          callback();
+        }, 600);
+      }
+
+    ], function(err, results) {
+
+      var end_time = Date.now();
+      var time_difference = end_time - start_time;
+
+      expect(err).to.not.be.ok();
+      expect(results).to.be.an('array');
+      expect(results[0]).to.not.be.ok();
+      expect(results[1]).to.not.be.ok();
+      expect(results[2]).to.not.be.ok();
+      expect(time_difference).to.be.greaterThan(199);
+      done();
+
+    });
+
+  });
+
+  it('should process each task in order', function(done) {
+
+    var start_time = Date.now();
+
+    async.waterfall([
+
+      function task1(callback) {
+        setTimeout(function() {
+          callback(null, ["task1"]);
+        }, 600);
+      },
+
+      function task2(results, callback) {
+        setTimeout(function() {
+          callback(null, results.concat("task2"));
+        }, 400);
+      },
+
+      function task3(results, callback) {
+        setTimeout(function() {
+          callback(null, results.concat("task3"));
+        }, 200);
+      }
+
+    ], function(err, results) {
+
+      var end_time = Date.now();
+      var time_difference = end_time - start_time;
+
+      expect(err).to.not.be.ok();
+      expect(results).to.be.an('array');
+      expect(results).to.eql(["task1", "task2", "task3"]);
+      expect(time_difference).to.be.greaterThan(1200);
+      done();
+
+    });
+
+  });
+
+  it('should stop processing the array of tasks when a task passes a truthy error value to the callback', function(done) {
+
+    var start_time = Date.now();
+
+    async.waterfall([
+
+      function task1(callback) {
+        setTimeout(function() {
+          callback(true, "task1");
+        }, 600);
+      },
+
+      function task2(callback) {
+        setTimeout(function() {
+          callback(null, "task2");
+        }, 400);
+      },
+
+      function task3(callback) {
+        setTimeout(function() {
+          callback(null, "task3");
+        }, 200);
+      }
+
+    ], function(err, results) {
+
+      var end_time = Date.now();
+      var time_difference = end_time - start_time;
+
+      expect(err).to.be.ok();
+      expect(results).to.be.ok();
+      expect(time_difference).to.be.lessThan(1000);
+      done();
+
+    });
+  });
+
+});