"navigation handlers are now added when impress is initialized"

js/impress.js

@@ -168,10 +168,20 @@
         transitionDuration: 1000
     };
     
+    var empty = function () { return false; };
+    
     var impress = window.impress = function ( rootId ) {
         
+        // if impress.js is not supported by the browser return a dummy API
+        // it may not be a perfect solution but we return early and avoid
+        // running code that may use features not implemented in the browser
         if (!impressSupported) {
-            return null;
+            return {
+                init: empty,
+                stepTo: empty,
+                prev: empty,
+                next: empty
+            };
         }
         
         rootId = rootId || "impress";
@@ -191,9 +201,9 @@
         
         // step events
         
-        var triggerEvent = function (el, eventName) {
+        var triggerEvent = function (el, eventName, detail) {
             var event = document.createEvent("CustomEvent");
-            event.initCustomEvent(eventName, true, true, {});
+            event.initCustomEvent(eventName, true, true, detail);
             el.dispatchEvent(event);
         };
         
@@ -342,7 +352,7 @@
             
             initialized = true;
             
-            triggerEvent(root, "impressInit");
+            triggerEvent(root, "impressInit", { api: roots[ "impress-root-" + rootId ] });
         };
         
         var stepTo = function ( el, force ) {
@@ -502,13 +512,6 @@
 (function ( document, window ) {
     'use strict';
     
-    var impress = window.impress;
-    
-    // if impress is not supported don't add any handlers
-    if (!impress.supported) {
-        return;
-    }
-    
     // throttling function calls, by Remy Sharp
     // http://remysharp.com/2010/07/21/throttling-function-calls/
     var throttle = function (fn, delay) {
@@ -522,6 +525,9 @@
         };
     };
     
+    document.addEventListener("impressInit", function (event) {
+        var api = event.detail.api;
+        
         // keyboard navigation handlers
         
         // prevent default keydown action when one of supported key is pressed
@@ -538,14 +544,14 @@
                     case 33: // pg up
                     case 37: // left
                     case 38: // up
-                         impress().prev();
+                             api.prev();
                              break;
                     case 9:  // tab
                     case 32: // space
                     case 34: // pg down
                     case 39: // right
                     case 40: // down
-                         impress().next();
+                             api.next();
                              break;
                 }
                 
@@ -572,7 +578,7 @@
                 }
             }
             
-        if ( impress().stepTo(target) ) {
+            if ( api.stepTo(target) ) {
                 event.stopImmediatePropagation();
                 event.preventDefault();
             }
@@ -587,7 +593,7 @@
                 target = target.parentNode;
             }
             
-        if ( impress().stepTo(target) ) {
+            if ( api.stepTo(target) ) {
                 event.preventDefault();
             }
         }, false);
@@ -600,9 +606,9 @@
                     result = null;
                     
                 if ( x < width ) {
-                result = impress().prev();
+                    result = api.prev();
                 } else if ( x > window.innerWidth - width ) {
-                result = impress().next();
+                    result = api.next();
                 }
                 
                 if (result) {
@@ -614,7 +620,10 @@
         // rescale presentation when window is resized
         window.addEventListener("resize", throttle(function () {
             // force going to active step again, to trigger rescaling
-        impress().stepTo( document.querySelector(".active"), true );
+            api.stepTo( document.querySelector(".active"), true );
         }, 250), false);
+        
+    }, false);
+        
 })(document, window);