function changeColor(dom,color,bg) {
    dom.style.color = color;
    dom.style.background = bg;
}
var spans = document.getElementsByTagName('span');

spans[0].onmouSEOver = function() {

changeColor(this,'red','#ddd');

}
spans[0].onmouSEOut = function() {

changeColor(this,'#333','#f5f5f5');

}
spans[1].onmouSEOver = function() {

changeColor(this.getElementsByTagName('strong')[0],'#ddd');

}

解耦，提取共同点