Apply before page exits

apply-before-exit.js

function applyBeforeExit(doBefore) {
    document.addEventListener("click", async (event) => {
        // Test for left click.
        if (event.button !== 0) {
            return;
        }

        let element = event.target;

        // Go up through the DOM tree to search for a link
        while (element && !element.hasAttribute("href")) {
            element = element.parentElement;
        }

        if (element) {
            const location = element.getAttribute("href");

            // If the link is for e-mail, phone or new window, do nothing
            if ((location && /^((mailto|tel):|#)/.test(location)) || element.hasAttribute("target")) {
                return;
            }

            event.preventDefault();

            try {
                await doBefore();
            } catch (_e) { /* empty */ }

            // Once callback returns a promise, go to the new page
            if (location) {
                window.location.assign(location);
            }
        }
    });
}