Looking for an unstable element which appears and disappears?

In Selenium, you can use the "Explicit Wait" functionality to wait for a specific condition to be met before proceeding with the execution of your script. The "ExpectedConditions" class provides a range of conditions that you can use to wait for elements to be visible, clickable, or present.

To wait for all activities and animations to complete before proceeding, you can use the "elementToBeClickable" condition on an element that you know will be clickable only after all animations and activities have finished. For example, you can wait for a "Submit" button to become clickable before proceeding:

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;

// ...

// Wait for up to 10 seconds for the Submit button to become clickable
WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement submitButton = wait.until(ExpectedConditions.elementToBeClickable(By.id("submit-button")));

This will wait for a maximum of 10 seconds for the element with ID "submit-button" to become clickable. If the element becomes clickable within this time, the script will proceed. If not, a TimeoutException will be raised.

Note that you may need to adjust the timeout value depending on the complexity of the animations and activities on your page.

What if it appeared once and removed from DOM, and appeared again?

If the element you are waiting for appears and disappears from the DOM multiple times, you can use a while loop to keep waiting until the element is present in the DOM.

Here's an example in Java that waits for an element with ID "my-dynamic-element" to appear and disappear from the DOM multiple times:

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;

// ...

// Wait for up to 10 seconds for the element with ID "my-dynamic-element" to appear in the DOM
WebDriverWait wait = new WebDriverWait(driver, 10);
while (true) {
    try {
        WebElement dynamicElement = wait.until(ExpectedConditions.presenceOfElementLocated(By.id("my-dynamic-element")));
        // Do something with the dynamic element
    } catch (Exception e) {
        // Element is not present in the DOM, handle the exception or break the loop
        // if you want to stop waiting
    }
}

In this example, we're using a while loop to keep waiting for the element to appear and disappear from the DOM. The loop will keep running until the element is found in the DOM. Once the element is present, we can perform some action with it.

If the element is not present in the DOM after the specified timeout, the until method will throw an exception, which we catch and handle in the catch block. You can choose to handle the exception or break the loop if you want to stop waiting.

Will there be a risk if the element is never appear again?

Yes, there is a risk of getting stuck in an infinite loop if the dynamic element never appears in the DOM. To prevent this, you can add a timeout to the loop and break out of it if the timeout is reached.

Here's an updated example in Java that waits for an element with ID "my-dynamic-element" to appear and disappear from the DOM multiple times, but breaks out of the loop after a maximum of 30 seconds:

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;

// ...

// Wait for up to 30 seconds for the element with ID "my-dynamic-element" to appear in the DOM
WebDriverWait wait = new WebDriverWait(driver, 30);
long startTime = System.currentTimeMillis();
while (System.currentTimeMillis() - startTime < 30000) { // Break out of the loop after 30 seconds
    try {
        WebElement dynamicElement = wait.until(ExpectedConditions.presenceOfElementLocated(By.id("my-dynamic-element")));
        // Do something with the dynamic element
        // ...
        break; // End the loop if we found the element and performed the necessary action
    } catch (Exception e) {
        // Element is not present in the DOM, handle the exception or continue waiting
        // ...
    }
}

In this updated example, we've added a startTime variable to track the start time of the loop and added a condition to break out of the loop if 30 seconds have passed since the start time. If the dynamic element is not found within the specified timeout, the loop will break and the script will continue executing after the loop.

You should adjust the timeout value to a reasonable value for your application, depending on how long you expect the dynamic element to appear and disappear from the DOM.