How to handle javascript alerts, confirmation and prompts?

Generally JavaScript popups are generated by web application and hence they can be easily controlled by the browser.

// Get a handle to the open alert, prompt or confirmation
Alert alert = driver.switchTo().alert();

Alert is an interface. There below are the methods that are used

//Will Click on OK button.
alert.accept();

// Will click on Cancel button.
alert.dismiss()

//will get the text which is present on th Alert.
alert.getText();

//Will pass the text to the prompt popup
alert.sendkeys();

//Is used to Authenticate by passing the credentials
alert.authenticateUsing(Credentials credentials)

Sample Program to handle alerts

package com.qaearth.test;
import org.openqa.selenium.Alert;
import org.openqa.selenium.By;
import org.openqa.selenium.firefox.FirefoxDriver;
public class PopupsHandling {
public static void main(String a[]) throws InterruptedException {
System.setProperty("webdriver.gecko.driver", "Drivers/geckodriver.exe");
FirefoxDriver driver = new FirefoxDriver();
driver.manage().window().maximize();
driver.navigate().to("https://qaearth.blogspot.in/p/testing-examples.html");
driver.findElement(By.cssSelector("#alert")).click();
Thread.sleep(2000);
Alert alert = driver.switchTo().alert();
System.out.println(alert.getText());
alert.sendKeys("Krishna");
alert.accept();
//alert.dismiss();
}
}