var aElems = document.getElementsByTagName("a"); 
for (var i=0, n=aElems.length; i<n; ++i) { 
    if (/(?:^|\s+)_blank(?:\s+|$)/.test(aElems[i].className)) { 
        aElems[i].onclick = function() { 
            return !window.open(this.href, "_blank"); 
        } 
    } 
}