TipsTricksTests.java

@Test
public void handleJavaScripPopUps() {
    driver.navigate().to("http://www.w3schools.com/js/tryit.asp?filename=tryjs_confirm");
    driver.switchTo().frame("iframeResult");
    var button = driver.findElement(By.xpath("/html/body/button"));
    button.click();
    Alert alert = driver.switchTo().alert();

    if (alert.getText().equals("Press a button!")) {
        alert.accept();
    }
    else {
        alert.dismiss();
    }
}