From 7279d2b20766554f660b431ce595342adcefec8b Mon Sep 17 00:00:00 2001
From: Luke Childs <lukechilds123@gmail.com>
Date: Wed, 22 Feb 2017 23:41:23 +0700
Subject: [PATCH 1/4] Add test for dataURL with callback always returning image
 data async

---
 test/canvas.test.js | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/canvas.test.js b/test/canvas.test.js
index 72bf6be..006e776 100644
--- a/test/canvas.test.js
+++ b/test/canvas.test.js
@@ -519,6 +519,14 @@ describe('Canvas', function () {
       });
     });
 
+    it('toDataURL(function (err, str) {...}) is async even with no canvas data', function (done) {
+      new Canvas().toDataURL(function(err, str){
+        assert.ifError(err);
+        assert.ok('data:,' === str);
+        done();
+      });
+    });
+
     it('toDataURL(0.5, function (err, str) {...}) works and defaults to PNG', function (done) {
       new Canvas(200,200).toDataURL(0.5, function(err, str){
         assert.ifError(err);

From f6d8214017508ea6eadb1fcd7491caaf99c3366b Mon Sep 17 00:00:00 2001
From: Luke Childs <lukechilds123@gmail.com>
Date: Wed, 22 Feb 2017 23:45:14 +0700
Subject: [PATCH 2/4] Return the no pixel string async if a callback was passed
 in

---
 lib/canvas.js | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/canvas.js b/lib/canvas.js
index 8272c9b..6a7de5c 100644
--- a/lib/canvas.js
+++ b/lib/canvas.js
@@ -231,11 +231,6 @@ Canvas.prototype.toDataURL = function(a1, a2, a3){
   // ['image/jpeg', qual, fn] -> ['image/jpeg', {quality: qual}, fn]
   // ['image/jpeg', undefined, fn] -> ['image/jpeg', null, fn]
 
-  if (this.width === 0 || this.height === 0) {
-    // Per spec, if the bitmap has no pixels, return this string:
-    return "data:,";
-  }
-
   var type = 'image/png';
   var opts = {};
   var fn;
@@ -264,6 +259,11 @@ Canvas.prototype.toDataURL = function(a1, a2, a3){
     }
   }
 
+  if (this.width === 0 || this.height === 0) {
+    // Per spec, if the bitmap has no pixels, return this string:
+    return fn ? fn(null, "data:,") : "data:,";
+  }
+
   if ('image/png' === type) {
     if (fn) {
       this.toBuffer(function(err, buf){

From 3bd0dffea82ecb3bc79fc936cb4c08ec991c0e1a Mon Sep 17 00:00:00 2001
From: Luke Childs <lukechilds123@gmail.com>
Date: Thu, 23 Feb 2017 00:18:51 +0700
Subject: [PATCH 3/4] Make sure callback isn't executed synchronously

---
 lib/canvas.js | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/canvas.js b/lib/canvas.js
index 6a7de5c..11aab6f 100644
--- a/lib/canvas.js
+++ b/lib/canvas.js
@@ -261,7 +261,13 @@ Canvas.prototype.toDataURL = function(a1, a2, a3){
 
   if (this.width === 0 || this.height === 0) {
     // Per spec, if the bitmap has no pixels, return this string:
-    return fn ? fn(null, "data:,") : "data:,";
+    if (fn) {
+      setTimeout(function() {
+        fn(null, "data:,");
+      });
+      return;
+    }
+    return "data:,";
   }
 
   if ('image/png' === type) {

From 818a26a43a8a5b1867e20d584b0a4423f9f6868b Mon Sep 17 00:00:00 2001
From: Luke Childs <lukechilds123@gmail.com>
Date: Thu, 23 Feb 2017 00:30:00 +0700
Subject: [PATCH 4/4] Return no canvas data string synchronously for backwards
 compatibility

---
 lib/canvas.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/canvas.js b/lib/canvas.js
index 11aab6f..efb873d 100644
--- a/lib/canvas.js
+++ b/lib/canvas.js
@@ -261,13 +261,13 @@ Canvas.prototype.toDataURL = function(a1, a2, a3){
 
   if (this.width === 0 || this.height === 0) {
     // Per spec, if the bitmap has no pixels, return this string:
+    var str = "data:,";
     if (fn) {
       setTimeout(function() {
-        fn(null, "data:,");
+        fn(null, str);
       });
-      return;
     }
-    return "data:,";
+    return str;
   }
 
   if ('image/png' === type) {