JS: how to trigger javascript when the content of the text box is cleared and the text box is cleared.

The text box to be filled in for multiple websites provides a default prompt language by default. when you click this text box, you can clear the default text, when you delete the entered text and leave the focus text box, you can write the default text into the text box. the text box to be filled in for multiple websites will provide a default prompt language by default, when you click this text box, you can clear the default text. when you delete the input text and the focus leaves the text box, you can write the default text to the text box.

The code is as follows:

 
 Click the text box to clear the default value