Merge pull request #46 from Medium/nick-spread

add spread() to kew

Author: nicks

kew.js

@@ -298,6 +298,36 @@ Promise.prototype.failBound = function (onFail, scope, var_args) {
   return promise
 }
 
+/**
+ * Spread a promises outputs to the functions arguments.
+ * @param {?function(this:void, ...): RESULT|undefined} onSuccess
+ * @return {!Promise.<RESULT>} returns a new promise with the output of the onSuccess or
+ *     onFail handler
+ * @template RESULT
+ */
+Promise.prototype.spread = function (onSuccess) {
+  return this.then(allInternal)
+  .then(function (array) {
+    return onSuccess.apply(null, array)
+  })
+}
+
+/**
+ * Spread a promises outputs to the functions arguments.
+ * @param {function(this:SCOPE, ...): RESULT} onSuccess
+ * @param {SCOPE} scope Object whose context callback will be executed in.
+ * @param {...*} var_args Additional arguments to be passed to the promise callback.
+ * @return {!Promise.<RESULT>} returns a new promise with the output of the onSuccess
+ * @template SCOPE, RESULT
+ */
+Promise.prototype.spreadBound = function (onSuccess, scope, var_args) {
+  var args = Array.prototype.slice.call(arguments, 2)
+  return this.then(allInternal)
+  .then(function (array) {
+    return onSuccess.apply(scope, args.concat(array))
+  })
+}
+
 /**
  * Provide a callback to be called whenever this promise is either resolved
  * or rejected.
@@ -604,6 +634,16 @@ function all(promises) {
   if (arguments.length != 1 || !Array.isArray(promises)) {
     promises = Array.prototype.slice.call(arguments, 0)
   }
+  return allInternal(promises)
+}
+
+/**
+ * A version of all() that does not accept var_args
+ *
+ * @param {!Array.<!Promise>} promises
+ * @return {!Promise.<!Array>}
+ */
+function allInternal(promises) {
   if (!promises.length) return resolve([])
 
   var outputs = []
@@ -676,6 +716,15 @@ function allSettled(promises) {
   return promise
 }
 
+/**
+ * Takes an array of results and spreads them to the arguments of a function.
+ * @param {!Array} array
+ * @param {!Function} fn
+ */
+function spread(array, fn) {
+  resolve(array).spread(fn)
+}
+
 /**
  * Create a new Promise which looks like a deferred
  *
@@ -788,6 +837,7 @@ module.exports = {
   , nfcall: nfcall
   , resolve: resolve
   , reject: reject
+  , spread: spread
   , stats: stats
   , allSettled: allSettled
   , Promise: Promise

test/spread.js

@@ -0,0 +1,35 @@
+var Q = require('../kew')
+
+exports.testSpreadStatic = function (test) {
+  Q.spread([Q.resolve('a'), 'b'], function (a, b) {
+    test.equal('a', a)
+    test.equal('b', b)
+    test.done()
+  })
+}
+
+exports.testSpreadMethod = function (test) {
+  Q.resolve(true)
+      .then(function () {
+        return ['a', 'b']
+      })
+      .spread(function (a, b) {
+        test.equal('a', a)
+        test.equal('b', b)
+        test.done()
+      })
+}
+
+exports.testSpreadBoundMethod = function (test) {
+  Q.resolve(true)
+      .then(function () {
+        return [Q.resolve('a'), 'b']
+      })
+      .spreadBound(function (c, a, b) {
+        test.equal('scope', this.scope)
+        test.equal('c', c)
+        test.equal('a', a)
+        test.equal('b', b)
+        test.done()
+      }, {scope: 'scope'}, 'c')
+}