In this case, the email validation appears to happen server-side, not client-side via JavaScript. The provided email is sent to a backend API, which determines what happens next, making the ...

For example, a list of e-mail addresses or previous URLs ... beta versions so that we can reduce the amount of JavaScript required for form validation. Because these are HTML tags, it doesn ...

their email address is checked against the attacker’s database, via JavaScript-based validation scripts on the page, before the fraudulent credential stealing login form is displayed.

Tcomb, a validation library for Node.js and browsers, is being offered as a tool for domain-driven design and runtime checking for JavaScript. According to GitHub-based documentation, the tcomb ...