Broader try-catch for handling impress-console-button disappearance (#652)

The previous attempt at merely reading a property of event.target was
incorrect. It worked at first but errors reappeared later, so must
have been a reace.

This wraps the entire navigation event handlers in the try-catch, and
then checks for the very specific error and suppresses it. Other errors
are rethrown as is.

js/impress.js

@@ -2965,16 +2965,6 @@
             // check if event target (or any of its parents is a link)
             var target = event.target;
             try {
-
-                // For example, when clicking on the button to launch speaker console, the button
-                // is immediately deleted from the DOM. In this case target is a DOM element when
-                // we get it, but turns out to be null if you try to actually do anything with it.
-                var foo = target.id; // jshint ignore:line
-            }
-            catch ( err ) {
-                return;
-            }
-
                 while ( ( target.tagName !== "A" ) &&
                         ( target !== document.documentElement ) ) {
                     target = target.parentNode;
@@ -2993,17 +2983,24 @@
                     event.stopImmediatePropagation();
                     event.preventDefault();
                 }
+            }
+            catch ( err ) {
+
+                // For example, when clicking on the button to launch speaker console, the button
+                // is immediately deleted from the DOM. In this case target is a DOM element when
+                // we get it, but turns out to be null if you try to actually do anything with it.
+                if ( err instanceof TypeError &&
+                     err.message === "target is null" ) {
+                    return;
+                }
+                throw err;
+            }
         }, false );
 
         // Delegated handler for clicking on step elements
         gc.addEventListener( document, "click", function( event ) {
             var target = event.target;
             try {
-                var foo = target.id; // jshint ignore:line
-            }
-            catch ( err ) {
-                return;
-            }
 
                 // Find closest step element that is not active
                 while ( !( target.classList.contains( "step" ) &&
@@ -3015,6 +3012,18 @@
                 if ( api.goto( target ) ) {
                     event.preventDefault();
                 }
+            }
+            catch ( err ) {
+
+                // For example, when clicking on the button to launch speaker console, the button
+                // is immediately deleted from the DOM. In this case target is a DOM element when
+                // we get it, but turns out to be null if you try to actually do anything with it.
+                if ( err instanceof TypeError &&
+                     err.message === "target is null" ) {
+                    return;
+                }
+                throw err;
+            }
         }, false );
 
         // Add a line to the help popup

src/plugins/navigation/navigation.js

@@ -125,16 +125,6 @@
             // check if event target (or any of its parents is a link)
             var target = event.target;
             try {
-
-                // For example, when clicking on the button to launch speaker console, the button
-                // is immediately deleted from the DOM. In this case target is a DOM element when
-                // we get it, but turns out to be null if you try to actually do anything with it.
-                var foo = target.id; // jshint ignore:line
-            }
-            catch ( err ) {
-                return;
-            }
-
                 while ( ( target.tagName !== "A" ) &&
                         ( target !== document.documentElement ) ) {
                     target = target.parentNode;
@@ -153,17 +143,24 @@
                     event.stopImmediatePropagation();
                     event.preventDefault();
                 }
+            }
+            catch ( err ) {
+
+                // For example, when clicking on the button to launch speaker console, the button
+                // is immediately deleted from the DOM. In this case target is a DOM element when
+                // we get it, but turns out to be null if you try to actually do anything with it.
+                if ( err instanceof TypeError &&
+                     err.message === "target is null" ) {
+                    return;
+                }
+                throw err;
+            }
         }, false );
 
         // Delegated handler for clicking on step elements
         gc.addEventListener( document, "click", function( event ) {
             var target = event.target;
             try {
-                var foo = target.id; // jshint ignore:line
-            }
-            catch ( err ) {
-                return;
-            }
 
                 // Find closest step element that is not active
                 while ( !( target.classList.contains( "step" ) &&
@@ -175,6 +172,18 @@
                 if ( api.goto( target ) ) {
                     event.preventDefault();
                 }
+            }
+            catch ( err ) {
+
+                // For example, when clicking on the button to launch speaker console, the button
+                // is immediately deleted from the DOM. In this case target is a DOM element when
+                // we get it, but turns out to be null if you try to actually do anything with it.
+                if ( err instanceof TypeError &&
+                     err.message === "target is null" ) {
+                    return;
+                }
+                throw err;
+            }
         }, false );
 
         // Add a line to the help popup