using the confirm method when leaving site

Question

I want a confirm message to popup when clicking on an external link. Though it doesnt want to work out. I dont get the confirm popup when i click on an external link. Any solutions ?

Javascript code

function warning(){
    var warning = confirm('Do you want to leave');
    if(!warning){
    alert("Staying on site");
    return false;
    } else {
        alert("Leaving site");
    return true;
    }
}

function init() {
    var warn = document.getElementsByTagName("ul");
    for(i=0; i<warn.length; i++)
        if(warn[i].className == "meny"){
            var link = document.getElementsByTagName("li");
    }
    for(i=0; i<link.length; i++){
        var links = document.getElementsByTagName("a");
        if(links[i].className == "external"){
            links.onclick = warning;
        }
    }
}

Html code:

<ul class="meny"">
<li><a class="external" href="https://www.mah.se">Mah</a></li>
<li><a class="external" href="https://www.google.se/">Google</a></li>
<li><a class="external" href="http://www.facebook.com/">Facebook</a></li>
<li><a class="external" href="http://www.youtube.com/">Youtube</a></li>
<li><a href="#">Digitalt</a></li>
<li><a href="#">Kultur</a></li>
<li><a href="#">Nöje</a></li>
<li><a href="#">Sport</a></li>
<li><a href="#">Familj</a></li>
<li><a href="#">Resor</a></li>
<li><a href="#">Inrikes</a></li>
<li><a href="#">Utrikes</a></li>
<li><a href="#">Jobb</a></li>
</ul>

Answer 1

This behavior can only be accomplished by handling the onbeforeunload event. Your handler should return a string, which is the message that appears to the user. A simple example:

window.onbeforeunload = function () {
    return 'are you sure you want to leave?';  
};

http://jsfiddle.net/rHkfM/

Answer 2

May I suggest to slightly modify your code:

function init() {
    var warn = document.getElementsByTagName("ul");
    for(i=0; i<warn.length; i++)
        if(warn[i].className == "meny"){
            var link = document.getElementsByTagName("li");
    }
    var links = document.getElementsByTagName("a");
    for(i=0; i<link.length; i++){
        if(links[i].className == "external"){
            links.external = true;
        }
    }
}

then add:

window.onbeforeunload = function (event) {
    if (event.srcElement.external)
        return 'are you sure you want to leave?';  
};

Please pay attention, this line:

    var links = document.getElementsByTagName("a");

must be outside the loop.