Rather than take a number to do more than one thing, also accept taking a list of functions to call on each thing.

isaacs · isaacs · commit 9a16d0ba7a04 · 2010-08-31T22:25:32.000-07:00
diff --git a/lib/utils/async-map.js b/lib/utils/async-map.js
@@ -2,22 +2,32 @@
 /*
 usage:
 
-asyncMap(myListOfStuff, function (thing, cb) { doSomething(thing, cb) }, cb)
-asyncMap(list, function (l, cb) { foo(l, cb) ; bar(l, cb) }, 2, cb)
+// do something to a list of things
+asyncMap(myListOfStuff, function (thing, cb) { doSomething(thing.foo, cb) }, cb)
+// do more than one thing to each item
+asyncMap(list, fooFn, barFn, cb)
+// call a function that needs to go in and call the cb 3 times
+asyncMap(list, callsMoreThanOnce, 3, cb)
 
 */
 
 module.exports = asyncMap
 
-function asyncMap (list, fn, n, cb_) {
-  if (typeof n === "function") cb_ = n, n = 1
+function asyncMap (list) {
+  var steps = Array.prototype.slice.call(arguments)
+    , list = steps.shift() || []
+    , cb_ = steps.pop()
   if (typeof cb_ !== "function") throw new Error(
     "No callback provided to asyncMap")
-  if (!list || !list.length) return cb_(null, [])
-  var data = []
+  if (!Array.isArray(list)) list = [list]
+  var n = (typeof steps[steps.length - 1] === "number")
+        ? steps.pop()
+        : steps.length
+    , data = []
     , errState = null
     , l = list.length
     , a = l * n
+  if (!a) return cb_(null, [])
   function cb (er, d) {
     if (errState) return
     if (arguments.length > 1) data = data.concat(d)
@@ -27,13 +37,20 @@ function asyncMap (list, fn, n, cb_) {
       a += (list.length - l) * n
       l = list.length
       process.nextTick(function () {
-        newList.forEach(function (ar) { fn(ar, cb) })
+        newList.forEach(function (ar) {
+          steps.forEach(function (fn) { fn(ar, cb) })
+        })
       })
     }
+    // allow the callback to return boolean "false" to indicate
+    // that an error should not tank the process.
     if (er) {
       if (false === cb_(errState = er, data)) errState = null
     } else if (-- a === 0) cb_(errState, data)
   }
-  list.forEach(function (ar) { fn(ar, cb) })
+  // expect the supplied cb function to be called
+  // "n" times for each thing in the array.
+  list.forEach(function (ar) {
+    steps.forEach(function (fn) { fn(ar, cb) })
+  })
 }
-
