Google is recommending that Web developers not use JavaScript dialog boxes, and it is proposing that Chromium no longer support this type of pop-up. The dialog boxes often appear when a user is about to leave a website, and they require that the user interact with the box in some way before being closed, a technique that is aggravating to Web users. Some developers have used the dialog boxes more nefariously in scareware or ransomware campaigns.
Right now, the only way for users to avoid the boxes is to disable JavaScript, which also prevents them from accessing a lot of useful features in Web apps.
Google is proposing some alternatives to the JavaScript dialog boxes that would be less susceptible to abuse.