added client side utils proxy method caller

@@ -247,9 +247,7 @@ Casper.prototype.back = function back() {
  */
 Casper.prototype.base64encode = function base64encode(url, method, data) {
     "use strict";
-    return this.evaluate(function _evaluate(url, method, data) {
-        return __utils__.getBase64(url, method, data);
-    }, url, method, data);
+    return this.callUtils("getBase64", url, method, data);
 };
 
 /**
@@ -268,6 +266,27 @@ Casper.prototype.bypass = function bypass(nb) {
 };
 
 /**
+ * Invokes a client side utils object method within the remote page, with arguments.
+ *
+ * @param  {String}   method  Method name
+ * @return {...args}          Arguments
+ * @return {Mixed}
+ * @throws {CasperError}      If invokation failed.
+ */
+Casper.prototype.callUtils = function callUtils(method) {
+    "use strict";
+    var args = [].slice.call(arguments, 1);
+    var result = this.evaluate(function(method, args) {
+        return __utils__.__call(method, args);
+    }, method, args);
+    if (utils.isObject(result) && result.__isCallError) {
+        throw new CasperError(f("callUtils(%s) with args %s thrown an error: %s",
+                              method, args, result.message));
+    }
+    return result;
+};
+
+/**
  * Proxy method for WebPage#render. Adds a clipRect parameter for
  * automatically set page clipRect setting values and sets it back once
  * done. If the cliprect parameter is omitted, the full page viewport
@@ -715,9 +734,7 @@ Casper.prototype.evaluateOrDie = function evaluateOrDie(fn, message, status) {
 Casper.prototype.exists = function exists(selector) {
     "use strict";
     this.checkStarted();
-    return this.evaluate(function _evaluate(selector) {
-        return __utils__.exists(selector);
-    }, selector);
+    return this.callUtils("exists", selector);
 };
 
 /**
@@ -742,9 +759,7 @@ Casper.prototype.exit = function exit(status) {
 Casper.prototype.fetchText = function fetchText(selector) {
     "use strict";
     this.checkStarted();
-    return this.evaluate(function _evaluate(selector) {
-        return __utils__.fetchText(selector);
-    }, selector);
+    return this.callUtils("fetchText", selector);
 };
 
 /**
@@ -1002,9 +1017,7 @@ Casper.prototype.getElementBounds = function getElementBounds(selector) {
     if (!this.exists(selector)) {
         throw new CasperError("No element matching selector found: " + selector);
     }
-    var clipRect = this.evaluate(function _evaluate(selector) {
-        return __utils__.getElementBounds(selector);
-    }, selector);
+    var clipRect = this.callUtils("getElementBounds", selector);
     if (!utils.isClipRect(clipRect)) {
         throw new CasperError('Could not fetch boundaries for element matching selector: ' + selector);
     }
@@ -1023,9 +1036,7 @@ Casper.prototype.getElementInfo = function getElementInfo(selector) {
     if (!this.exists(selector)) {
         throw new CasperError(f("Cannot get informations from %s: element not found.", selector));
     }
-    return this.evaluate(function(selector) {
-        return __utils__.getElementInfo(selector);
-    }, selector);
+    return this.callUtils("getElementInfo", selector);
 };
 
 /**
@@ -1040,9 +1051,7 @@ Casper.prototype.getElementsInfo = function getElementsInfo(selector) {
     if (!this.exists(selector)) {
         throw new CasperError(f("Cannot get information from %s: no elements found.", selector));
     }
-    return this.evaluate(function(selector) {
-        return __utils__.getElementsInfo(selector);
-    }, selector);
+    return this.callUtils("getElementsInfo", selector);
 };
 
 /**
@@ -1057,9 +1066,7 @@ Casper.prototype.getElementsBounds = function getElementBounds(selector) {
     if (!this.exists(selector)) {
         throw new CasperError("No element matching selector found: " + selector);
     }
-    return this.evaluate(function _evaluate(selector) {
-        return __utils__.getElementsBounds(selector);
-    }, selector);
+    return this.callUtils("getElementsBounds", selector);
 };
 
 /**
@@ -1074,9 +1081,7 @@ Casper.prototype.getFormValues = function(selector) {
     if (!this.exists(selector)) {
         throw new CasperError(f('Form matching selector "%s" not found', selector));
     }
-    return this.evaluate(function(selector) {
-        return __utils__.getFormValues(selector);
-    }, selector);
+    return this.callUtils("getFormValues", selector);
 };
 
 /**
@@ -1328,9 +1333,7 @@ Casper.prototype.mouseEvent = function mouseEvent(type, selector) {
     if (!this.exists(selector)) {
         throw new CasperError(f("Cannot dispatch %s event on nonexistent selector: %s", type, selector));
     }
-    if (this.evaluate(function(type, selector) {
-        return window.__utils__.mouseEvent(type, selector);
-    }, type, selector)) {
+    if (this.callUtils("mouseEvent", type, selector)) {
         return true;
     }
     // fallback onto native QtWebKit mouse events
@@ -1941,9 +1944,7 @@ Casper.prototype.viewport = function viewport(width, height, then) {
 Casper.prototype.visible = function visible(selector) {
     "use strict";
     this.checkStarted();
-    return this.evaluate(function _evaluate(selector) {
-        return __utils__.visible(selector);
-    }, selector);
+    return this.callUtils("visible", selector);
 };
 
 /**

@@ -59,6 +59,26 @@
         // public members
         this.options = options || {};
         this.options.scope = this.options.scope || document;
+
+        /**
+         * Calls a method part of the current prototype, with arguments.
+         *
+         * @param  {String} method Method name
+         * @param  {Array}  args   arguments
+         * @return {Mixed}
+         */
+        this.__call = function __call(method, args) {
+            if (method === "__call") {
+                return;
+            }
+            try {
+                return this[method].apply(this, args);
+            } catch (err) {
+                err.__isCallError = true;
+                return err;
+            }
+        };
+
         /**
          * Clicks on the DOM element behind the provided selector.
          *

+/*global casper*/
+/*jshint strict:false*/
+casper.test.begin('Casper.callUtils()', 2, function(test) {
+    casper.start("tests/site/index.html", function(){
+        this.evaluate(function() {
+            /*global __utils__*/
+            __utils__.testCallUtils = function() {
+                return [].slice.call(arguments);
+            };
+        });
+
+        test.assertEquals(casper.callUtils("testCallUtils", "a", "b", "c"),
+                          ["a", "b", "c"],
+                          "Casper.callUtils() invokes a client side utility");
+
+        test.assertThrows(casper.callUtils, ["xxx", "a", "b", "c"],
+            "Casper.callUtils() raises an error if used inappropriately");
+    });
+
+    casper.run(function() {
+        test.done();
+    });
+});