--- /dev/null
+
+/*
+usage:
+
+// 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)
+
+*/
+
+module.exports = asyncMap
+
+function asyncMap () {
+ 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) return cb_(null, [])
+ if (!Array.isArray(list)) list = [list]
+ var n = steps.length
+ , data = [] // 2d array
+ , errState = null
+ , l = list.length
+ , a = l * n
+ if (!a) return cb_(null, [])
+ function cb (er) {
+ if (er && !errState) errState = er
+
+ var argLen = arguments.length
+ for (var i = 1; i < argLen; i ++) if (arguments[i] !== undefined) {
+ data[i - 1] = (data[i - 1] || []).concat(arguments[i])
+ }
+ // see if any new things have been added.
+ if (list.length > l) {
+ var newList = list.slice(l)
+ a += (list.length - l) * n
+ l = list.length
+ process.nextTick(function () {
+ newList.forEach(function (ar) {
+ steps.forEach(function (fn) { fn(ar, cb) })
+ })
+ })
+ }
+
+ if (--a === 0) cb_.apply(null, [errState].concat(data))
+ }
+ // 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) })
+ })
+}