ensure explicitly setting viewportUseIntersectionObserver is not allo…

…wed (#147)

README.md

@@ -89,7 +89,6 @@ export default Component.extend(InViewportMixin, {
       viewportEnabled                 : true,
       viewportUseRAF                  : true,
       viewportSpy                     : false,
-      viewportUseIntersectionObserver : true,
       viewportScrollSensitivity       : 1,
       viewportRefreshRate             : 150,
       intersectionThreshold           : 0,
@@ -114,8 +113,9 @@ export default Component.extend(InViewportMixin, {
 - `viewportUseIntersectionObserver: boolean`
 
   Default: Depends on browser
+  Read-only
 
-  The Mixin by default will use the IntersectionObserver API. If IntersectionObserver is not supported in the target browser, ember-in-viewport will fallback to rAF.
+  The Mixin by default will use the IntersectionObserver API. If IntersectionObserver is not supported in the target browser, ember-in-viewport will fallback to rAF.  We prevent users from explicitly setting this to `true` as browsers lacking support for IntersectionObserver will throw an error.
 
   (https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API)
   (https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver/thresholds#Browser_compatibility)
@@ -191,7 +191,6 @@ module.exports = function(environment) {
       viewportEnabled                 : false,
       viewportUseRAF                  : true,
       viewportSpy                     : false,
-      viewportUseIntersectionObserver : true,
       viewportScrollSensitivity       : 1,
       viewportRefreshRate             : 100,
       viewportListeners               : [],

addon/mixins/in-viewport.js

@@ -54,13 +54,17 @@ export default Mixin.create({
     // ensure this mixin runs first, then your component can override the options
     this._super(...arguments);
 
-    const options = assign({
+    let options = assign({
       viewportUseRAF: canUseRAF(),
-      viewportUseIntersectionObserver: canUseIntersectionObserver(),
       viewportEntered: false,
       viewportListeners: []
     }, this._buildOptions());
 
+    // set viewportUseIntersectionObserver after merging users config to avoid errors in browsers that lack support (https://github.com/DockYard/ember-in-viewport/issues/146)
+    options = assign(options, {
+      viewportUseIntersectionObserver: canUseIntersectionObserver(),
+    });
+
     setProperties(this, options);
     set(this, '_evtListenerClosures', []);
   },