From 1aefb22789793cbfe3f51ede79a42aa63eccf8df Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@github.com>
Date: Fri, 23 Oct 2015 18:13:30 -0600
Subject: [PATCH] Add ViewRegistry.prototype.getNextUpdatePromise

Signed-off-by: Max Brunsfeld <maxbrunsfeld@github.com>
---
 spec/view-registry-spec.coffee | 18 ++++++++++++++++++
 src/view-registry.coffee       |  7 +++++++
 2 files changed, 25 insertions(+)

diff --git a/spec/view-registry-spec.coffee b/spec/view-registry-spec.coffee
index fcddd325a..a2b4965a5 100644
--- a/spec/view-registry-spec.coffee
+++ b/spec/view-registry-spec.coffee
@@ -209,3 +209,21 @@ describe "ViewRegistry", ->
       window.dispatchEvent(new UIEvent('resize'))
 
       expect(events).toEqual ['poll 1', 'poll 2']
+
+  describe "::getNextUpdatePromise()", ->
+    it "returns a promise that resolves at the end of the next update cycle", ->
+      updateCalled = false
+      readCalled = false
+      pollCalled = false
+
+      waitsFor 'getNextUpdatePromise to resolve', (done) ->
+        registry.getNextUpdatePromise().then ->
+          expect(updateCalled).toBe true
+          expect(readCalled).toBe true
+          expect(pollCalled).toBe true
+          done()
+
+        registry.updateDocument -> updateCalled = true
+        registry.readDocument -> readCalled = true
+        registry.pollDocument -> pollCalled = true
+        registry.pollAfterNextUpdate()
diff --git a/src/view-registry.coffee b/src/view-registry.coffee
index 3a46aa87a..c21622c04 100644
--- a/src/view-registry.coffee
+++ b/src/view-registry.coffee
@@ -195,6 +195,10 @@ class ViewRegistry
   pollAfterNextUpdate: ->
     @performDocumentPollAfterUpdate = true
 
+  getNextUpdatePromise: ->
+    @nextUpdatePromise ?= new Promise (resolve) =>
+      @resolveNextUpdatePromise = resolve
+
   clearDocumentRequests: ->
     @documentReaders = []
     @documentWriters = []
@@ -220,6 +224,9 @@ class ViewRegistry
     # process updates requested as a result of reads
     writer() while writer = @documentWriters.shift()
 
+    @nextUpdatePromise = null
+    @resolveNextUpdatePromise?()
+
   startPollingDocument: ->
     window.addEventListener('resize', @requestDocumentPoll)
     @observer.observe(document, {subtree: true, childList: true, attributes: true})