Executing JavaScript in Selenium Java

Introduction

Sometimes, Selenium cannot perform certain actions directly. Executing JavaScript helps control the browser in ways Selenium alone cannot.

When clicking a button that Selenium's click() cannot reach.

To scroll the page to a specific position.

To get or set values of elements not accessible by Selenium methods.

To change the style or attributes of elements dynamically during tests.

To trigger browser alerts or confirm dialogs.

Syntax

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("javascript code here");

You must cast the WebDriver instance to JavascriptExecutor.

The executeScript method runs JavaScript code in the browser context.

Examples

This example shows how to display a browser alert using JavaScript.

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("alert('Hello from JavaScript!')");

This scrolls the page down by 500 pixels vertically.

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("window.scrollBy(0, 500);");

This adds a red border around a specific element to highlight it.

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
WebElement element = driver.findElement(By.id("myElement"));
js.executeScript("arguments[0].style.border='3px solid red';", element);

Sample Program

This test opens a webpage, scrolls down, highlights the main heading by changing its background color, and prints the page title using JavaScript execution.

Selenium Java

import org.openqa.selenium.By;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;

public class ExecuteJavaScriptExample {
    public static void main(String[] args) {
        System.setProperty("webdriver.chrome.driver", "path/to/chromedriver");
        WebDriver driver = new ChromeDriver();
        try {
            driver.get("https://www.example.com");

            JavascriptExecutor js = (JavascriptExecutor) driver;

            // Scroll down 300 pixels
            js.executeScript("window.scrollBy(0,300);");

            // Find element and highlight it
            WebElement heading = driver.findElement(By.tagName("h1"));
            js.executeScript("arguments[0].style.backgroundColor = 'yellow';", heading);

            // Get page title using JavaScript
            String title = (String) js.executeScript("return document.title;");
            System.out.println("Page title is: " + title);

        } finally {
            driver.quit();
        }
    }
}

Important Notes

Always cast your WebDriver to JavascriptExecutor before running JavaScript.

Use arguments[0], arguments[1], etc., to pass WebElements or values safely into the script.

Be careful with JavaScript code syntax; errors can cause test failures.

Summary

Executing JavaScript lets you do things Selenium cannot do directly.

Use JavascriptExecutor and executeScript() method to run JavaScript in the browser.

Pass WebElements as arguments to manipulate page elements safely.