SOURCE

var links = document.getElementByTagName("a");
for(var i = 0; i< links.length;i++){
    if(links.getAttribute("class") =="popup") {
        links[i].onclick = function(){
            popUp(this.getAttribute("href"));
            return false;
}
}
}

<a href="https://cn.bing.com/" class='popup'>cess</a>