Table隔行变色

 function showtable(){
var color1 = "rgb(234,240,255)";
var color2 = "rgb(255,255,255)";
var bgColor = "rgb(255,255,193)";
var trs = document.getElementById("datatable").getElementsByTagName("tr");
for (var i=0;i<trs.length-1;i++){
if (i%2==0) {
trs[i].style.backgroundColor=color1;
trs[i]. = function(){
this.style.backgroundColor = bgColor;
}
trs[i]. = function(){
this.style.backgroundColor = color1;
}
} else {
trs[i].style.backgroundColor=color2;
trs[i]. = function(){
this.style.backgroundColor = bgColor;
}
trs[i]. = function(){
this.style.backgroundColor = color2;
}
}
}
}