在鼠标悬停在某个表格行的上方时改变该行文本效果

function highlightRows() {
    if(!document.getElementsByTagName) return false;
    var rows = document.getElementsByTagName("tr");
    for(var i=0;i<rows.length;i++){
        rows[i].onmouseover =  function () {
            this.style.fontWeight = "bold";
        }
        rows[i].onmouseout = function () {
            this.style.fontWeight = "normal";
        }
    }
}