Only write Orientation value if the offset exists.

blueimp · blueimp · commit 91609b6e3511 · 2020-05-04T14:53:12.000+09:00
diff --git a/README.md b/README.md
@@ -854,7 +854,10 @@ loadImage(
 
 **Please note:**  
 The Exif writer relies on the Exif tag offsets being available as
-`data.exifOffsets` property.
+`data.exifOffsets` property, which requires that Exif data has been parsed from
+the image.  
+The Exif writer can only change existing values, not add new tags, e.g. it
+cannot add an Exif `Orientation` tag for an image that does not have one.
 
 ### IPTC parser
 
diff --git a/js/load-image-exif.js b/js/load-image-exif.js
@@ -431,7 +431,9 @@
   loadImage.exifWriters = {
     // Orientation writer:
     0x0112: function (buffer, data, value) {
-      var view = new DataView(buffer, data.exifOffsets[0x0112] + 8, 2)
+      var orientationOffset = data.exifOffsets[0x0112]
+      if (!orientationOffset) return buffer
+      var view = new DataView(buffer, orientationOffset + 8, 2)
       view.setUint16(0, value, data.exifLittleEndian)
       return buffer
     }
