The onfocusin event triggers when an element is to lose focus. You can try to run the following code to learn how to implement onfocusout event in JavaScript.
Example
<!DOCTYPE html> <html> <body> <p>Write below:</p> <p>After losing focus, the background color of input check will change.</p> <input type = "text" onfocusout = "newFunc(this)"> <script> function newFunc(x) { x.style.background = "blue"; } </script> </body> </html>