Merge pull request #10 from xuxihai123/master

Support an initialization parameter

.gitignore

@@ -1,2 +1,4 @@
 node_modules
 npm-debug.log
+.idea
+yarn.lock

index.js

@@ -1,8 +1,8 @@
 'use strict'
 
-module.exports = function promiseWaterfall (callbacks) {
+module.exports = function promiseWaterfall (callbacks, initialArgs) {
   // Don't assume we're running in an environment with promises
   return callbacks.reduce(function (accumulator, callback) {
     return accumulator.then(callback)
-  }, Promise.resolve())
+  }, Promise.resolve(initialArgs))
 }

test.js

@@ -34,6 +34,18 @@ test('run array of promises sequentially', function (t) {
     })
 })
 
+test('run array of promises sequentially with an initialization parameter', function (t) {
+  t.plan(1)
+
+  return promiseWaterfall([
+    addOne,
+    addTwo
+  ], 10)
+    .then(function (sum) {
+      t.equals(sum, 13)
+    })
+})
+
 test('run array consisting of zero promises', function (t) {
   t.plan(1)