function targetBlank() 
{ 
    var links = document.getElementsByTagName("a"); 

    for (var i = 0; i < links.length; i++) 
    { 
        var link = links[i]; 
         
        if (link.getAttribute("href") && link.getAttribute("rel") == "external") 
        { 
            link.target = "_blank"; 
        } 
    } 
}