function fillSearch() {
    var s = document.getElementById("s");
        
    s.value = "Zoeken";
    s.onfocus = function() {
        if (s.value == 'Zoeken') {s.value = '';}
    };
    s.onblur = function() {
        if (s.value == '') {s.value = 'Zoeken';}
    };
}

window.onload = fillSearch;