How can I print a specific message on close of browser tab?

Question

I would like to print a message on the close of the browser tab. Something like this:

Please don't close this tab.....an important file is running on the same tab............closing this may lose the data

How do I do it?

Answer 1

You can use window.onbeforeunload

window.onbeforeunload = function(e){
    return "Do you want to close?";
}