[melky]

var arayLink = document.getElementsByTagName('a'),

ай-ай-ай

var a = /jpg$/,
    b, // current a
    c = 0,
    ie = !document.documentElement.addEventListener,
    handler = function(e){
        
        if (a.test( (event ? event.srcElement:e.target).href)) {
            alert("содержит");
        } else {
            alert("нет");
        }
    }

while ( b = document.links[c++] ) 
    ie ? b.attachEvent("onmouseover", handler ):b.addEventListener("mouseover",handler,false);

пример :

<a href="/mk" style="color:red">no jpg</a>
<a href="/lol.jpg" style="color:green">jpg</a>
<script>
var a = /jpg$/,
    b, // current a
    c = 0,
    ie = !document.documentElement.addEventListener,
    handler = function(e){
        
        if (a.test( (event ? event.srcElement:e.target).href)) {
            alert("содержит");
        } else {
            alert("нет");
        }
    }

while ( b = document.links[c++] ) 
    ie ? b.attachEvent("onmouseover", handler ):b.addEventListener("mouseover",handler,false);
</script>