diff --git a/examples/unrandomize.js b/examples/unrandomize.js
new file mode 100644
index 00000000000..fc8df3fcd1e
--- /dev/null
+++ b/examples/unrandomize.js
@@ -0,0 +1,33 @@
+/**
+ * Copyright 2017 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+var Browser = require('../lib/Browser');
+var browser = new Browser();
+
+browser.newPage().then(async page => {
+    await page.evaluateOnInitialized(function() {
+        Math.random = () => 42 / 100;
+    });
+    var result = await page.navigate('http://ariya.github.com/js/random/');
+    if (result) {
+        console.log(await page.evaluate(function () {
+            return document.getElementById('numbers').textContent;
+        }));
+    } else {
+        console.log('Network error.');
+    }
+    browser.close();
+});
diff --git a/lib/Page.js b/lib/Page.js
index c161798cc7d..9e52fd41082 100644
--- a/lib/Page.js
+++ b/lib/Page.js
@@ -304,6 +304,18 @@ class Page extends EventEmitter {
         return response.result.value;
     }
 
+    /**
+     * @param {function()} fun
+     * @param {!Array<*>} args
+     * @return {!Promise}
+     */
+    async evaluateOnInitialized(fun, ...args) {
+        var code = helpers.evaluationString(fun, args, false);
+        await this._client.send('Page.addScriptToEvaluateOnLoad', {
+            scriptSource: code
+        });
+    }
+
     /**
      * @param {!Page.ScreenshotType} screenshotType
      * @param {?{x: number, y: number, width: number, height: number}} clipRect
diff --git a/lib/helpers.js b/lib/helpers.js
index b5a868e0f3b..d7a19c1ce29 100644
--- a/lib/helpers.js
+++ b/lib/helpers.js
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-module.exports = {
+var helpers = module.exports = {
     /**
      * @param {!CDP} client
      * @param {string} url
@@ -53,16 +53,28 @@ module.exports = {
      * @return {!Promise<!Object>}
      */
     evaluate: function(client, fun, args, awaitPromise, sourceURL) {
-        var argsString = args.map(x => JSON.stringify(x)).join(',');
-        var code = `(${fun.toString()})(${argsString})`;
-        if (awaitPromise)
-            code = `Promise.resolve(${code})`;
-        if (sourceURL)
-            code += `\n//# sourceURL=${sourceURL}`;
+        var code = helpers.evaluationString(fun, args, awaitPromise, sourceURL);
         return client.send('Runtime.evaluate', {
             expression: code,
             awaitPromise: awaitPromise,
             returnByValue: true
         });
     },
+
+    /**
+     * @param {function()} fun
+     * @param {!Array<*>} args
+     * @param {boolean} awaitPromise
+     * @param {string=} sourceURL
+     * @return {string}
+     */
+    evaluationString: function(fun, args, awaitPromise, sourceURL) {
+        var argsString = args.map(x => JSON.stringify(x)).join(',');
+        var code = `(${fun.toString()})(${argsString})`;
+        if (awaitPromise)
+            code = `Promise.resolve(${code})`;
+        if (sourceURL)
+            code += `\n//# sourceURL=${sourceURL}`;
+        return code;
+    }
 }