Because confirm is a blocking function (no javascript will run until it returns true/false), and alertify is non-blocking (JS keeps executing). Alertify does not immediately return a true/false, but instead, it probably returns undefined immediately, then it calls a callback function later, after the user clicks OK or Cancel. The return value from that callback function has no effect in your example, because the onclick code has already finished running (because it is non-blocking).
Assuming you are using this: https://github.com/fabien-d/alertify.js/
This is how it actually works with a callback function, not a return value:
alertify.confirm( message, function (e) {
if (e) {
//after clicking OK
} else {
//after clicking Cancel
}
});
For your code sample, you might try something like this:
function performDelete ( a_element ) {
// perform your delete here
// a_element is the <a> tag that was clicked
}
function confirmAction ( a_element, message, action ) {
alertify.confirm(message, function(e) {
if (e) {
// a_element is the <a> tag that was clicked
if (action) {
action(a_element);
}
}
});
}
<a href="#" onclick="confirmAction(this, 'Are you sure you wish to remove this?', performDelete); return false;">Delete</a>
EDIT: updated to be a generic confirm dialog that calls a callback function if the user clicks ok.