added an exception class, alert when trying to navigate to non-existant pages (will improve the crappy alerts...)

lib/ComicBook.js

@@ -40,6 +40,25 @@ function merge(a, b) {
 	return b;
 }
 
+/**
+ * Exception class. Always throw an instance of this when throwing exceptions.
+ *
+ * @param {String} type
+ * @param {mixed} object
+ * @returns {ComicBookException}
+ */
+function ComicBookException(type, object) {
+
+	this.type = type;
+	this.object = object;
+
+	this.INVALID_PAGE = "invalid page";
+	this.INVALID_PAGE_TYPE = "invalid page type";
+	this.UNDEFINED_CONTROL = "undefined control";
+	this.INVALID_ZOOM_MODE = "invalid zoom mode";
+	this.INVALID_NAVIGATION_EVENT = "invalid navigation event";
+};
+
 function ComicBook(id, srcs, opts) {
 
 	var canvas_id = id;		// canvas element id
@@ -251,7 +270,7 @@ function ComicBook(id, srcs, opts) {
 	ComicBook.prototype.getControl = function(control) {
 
 		if (typeof this.control[control] === "undefined") {
-			throw "invalid control: " + control;
+			throw new ComicBookException(ComicBookException.UNDEFINED_CONTROL, control);
 		}
 
 		return this.control[control];
@@ -283,7 +302,7 @@ function ComicBook(id, srcs, opts) {
 		if (typeof pages[i] === "object") {
 			return pages[i];
 		} else {
-			throw "Invalid page index: " + i;
+			throw new ComicBookException(ComicBookException.INVALID_PAGE, i);
 		}
 	};
 
@@ -377,10 +396,13 @@ function ComicBook(id, srcs, opts) {
 
 		var zoom_scale;
 		var offsetW = 0, offsetH = 0;
+
 		var page = this.getPage(pointer);
 		var page2 = this.getPage(pointer + 1);
 
-		if (typeof page !== "object") { throw "invalid page type '"+ typeof page +"'"; }
+		if (typeof page !== "object") {
+			throw new ComicBookException(ComicBookException.INVALID_PAGE_TYPE, typeof page);
+		}
 
 		var width = page.width;
 
@@ -416,7 +438,7 @@ function ComicBook(id, srcs, opts) {
 				break;
 
 			default:
-				throw "invalid zoomMode";
+				throw new ComicBookException(ComicBookException.INVALID_ZOOM_MODE, options.zoomMode);
 		}
 
 		var canvas_width  = page.width * zoom_scale;
@@ -486,9 +508,17 @@ function ComicBook(id, srcs, opts) {
 	 * @see #drawPage
 	 */
 	ComicBook.prototype.drawNextPage = function () {
-		if (pointer + 1 < pages.length) {
+		try {
-			pointer += (options.displayMode === "single" || is_double_page_spread) ? 1 : 2;
+			if (pointer + 1 < pages.length) {
-			this.drawPage();
+				pointer += (options.displayMode === "single" || is_double_page_spread) ? 1 : 2;
+				this.drawPage();
+			}
+		} catch (e) {
+			if (e.type === ComicBookException.INVALID_PAGE) {
+				alert("you are at the end of the comic");
+			} else {
+				throw e;
+			}
 		}
 	};
 
@@ -498,12 +528,19 @@ function ComicBook(id, srcs, opts) {
 	 * @see #drawPage
 	 */
 	ComicBook.prototype.drawPrevPage = function () {
+		try {
+			is_double_page_spread = (this.getPage(pointer-1).width > this.getPage(pointer-1).height); // need to run double page check again here as we are going backwards
 
-		is_double_page_spread = (this.getPage(pointer-1).width > this.getPage(pointer-1).height); // need to run double page check again here as we are going backwards
+			if (pointer > 0) {
-
+				pointer -= (options.displayMode === "single" || is_double_page_spread) ? 1 : 2;
-		if (pointer > 0) {
+				this.drawPage();
-			pointer -= (options.displayMode === "single" || is_double_page_spread) ? 1 : 2;
+			}
-			this.drawPage();
+		} catch (e) {
+			if (e.type === ComicBookException.INVALID_PAGE) {
+				alert("you are at the start of the comic");
+			} else {
+				throw e;
+			}
 		}
 	};
 
@@ -629,7 +666,9 @@ function ComicBook(id, srcs, opts) {
 				}
 				break;
 			default:
-				throw "invalid navigation event: " + e.type;
+				throw new ComicBookException(
+					ComicBookException.INVALID_NAVIGATION_EVENT, e.type
+				);
 		}
 
 		if (side) {