window.onload= function(){
     var n = 0;
     var oTab = document.getElementById('pixel_canvas');
     var cTr = document.createElement('tr');
     var cTd = document.createElement('td');
     for (var i = 0; i <= 8; i++) {
         oTab.appendChild(cTr);
     }

 }

運(yùn)行后只有一個tr標(biāo)簽。