diff --git a/ChangeLog b/ChangeLog
index 386f1ab1..5f44286e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -15,6 +15,7 @@ Version 1.3.0
     New features
 
       * Presistent cookie support using --cookies=cookies.ini
+      * Added callback for page initialization (issue 143)
 
     Examples
 
diff --git a/examples/unrandomize.js b/examples/unrandomize.js
new file mode 100644
index 00000000..b1bcab25
--- /dev/null
+++ b/examples/unrandomize.js
@@ -0,0 +1,24 @@
+// Modify global object at the page initialization.
+// In this example, effectively Math.random() always returns 0.42.
+
+var page = new WebPage();
+
+page.onInitialized = function () {
+    page.evaluate(function () {
+        Math.random = function() {
+            return 42 / 100;
+        };
+    });
+};
+
+page.open('http://ariya.github.com/js/random/', function (status) {
+    var result;
+    if (status !== 'success') {
+        console.log('Network error.');
+    } else {
+        console.log(page.evaluate(function () {
+            return document.getElementById('numbers').textContent;
+        }));
+    }
+    phantom.exit();
+});
diff --git a/src/bootstrap.js b/src/bootstrap.js
index 229457d7..16d82852 100644
--- a/src/bootstrap.js
+++ b/src/bootstrap.js
@@ -19,6 +19,8 @@ window.WebPage = function() {
     // deep copy
     page.settings = JSON.parse(JSON.stringify(phantom.defaultPageSettings));
 
+    defineSetter("onInitialized", "initialized");
+
     defineSetter("onLoadStarted", "loadStarted");
 
     defineSetter("onLoadFinished", "loadFinished");
diff --git a/src/webpage.cpp b/src/webpage.cpp
index 2944bd5e..0c96a685 100644
--- a/src/webpage.cpp
+++ b/src/webpage.cpp
@@ -104,6 +104,7 @@ WebPage::WebPage(QObject *parent)
     m_webPage = new CustomPage(this);
     m_mainFrame = m_webPage->mainFrame();
 
+    connect(m_mainFrame, SIGNAL(javaScriptWindowObjectCleared()), SIGNAL(initialized()));
     connect(m_webPage, SIGNAL(loadStarted()), SIGNAL(loadStarted()));
     connect(m_webPage, SIGNAL(loadFinished(bool)), SLOT(finish(bool)));
 
diff --git a/src/webpage.h b/src/webpage.h
index 83c13056..8be197c8 100644
--- a/src/webpage.h
+++ b/src/webpage.h
@@ -86,6 +86,7 @@ public slots:
 	void mouseMoveTo(int x, int y);
 
 signals:
+    void initialized();
     void loadStarted();
     void loadFinished(const QString &status);
     void javaScriptAlertSent(const QString &msg);