Add waitForNthSelector.

lib/webpage.js

@@ -298,6 +298,41 @@
                     setTimeout(testForSelector, timeoutInterval);
                 },
 
+                //waits for selector to appear, then executes callbackFn
+                waitForNthSelector:function (selector, count, callbackFn, timeout) {
+                    var self = this,
+                        startTime = Date.now(),
+                        timeoutInterval = 150,
+                        testRunning = false,
+                    //if evaluate succeeds, invokes callback w/ true, if timeout,
+                    // invokes w/ false, otherwise just exits
+                        testForSelector = function () {
+
+                            var elapsedTime = Date.now() - startTime;
+
+                            if (elapsedTime > timeout) {
+                                self.options.debug && console.log('warning: timeout occurred while waiting for selector:"%s"'.yellow, selector);
+                                callbackFn(false);
+                                return;
+                            }
+
+                            self.evaluate(function (selectorToEvaluate) {
+                                return document.querySelectorAll(selectorToEvaluate).length;
+                            }, function (result) {
+                                testRunning = false;
+                                if (result >= count) {//selector found
+                                    callbackFn(true);
+                                }
+                                else {
+                                    setTimeout(testForSelector, timeoutInterval);
+                                }
+                            }, selector);
+                        };
+
+                    timeout = timeout || 10000; //default timeout is 2 sec;
+                    setTimeout(testForSelector, timeoutInterval);
+                },
+
                 injectJs:function (filename, callbackFn) {
 
                     executeMethod.call(this, '/page/functions/injectJs', callbackFn, filename);