急table添加tr一直报错,

急,table添加tr一直报错,请教高手,在线等
var   table   =   document.getElementById( "FOLDER ");
var   tr   =   document.createElement( "tr ");
var   td   =   document.createElement( "td ");
var   text1   =   document.createTextNode( "wwww ");
td.appendChild(text1);
tr.appendChild(td);

table.appendChild(tr);//这行一直报错

错误信息:意外地调用了方法或属性访问

[解决办法]
var tr = table.inserRow(table.rows.length);
var td = tr.insertCell(0);
td.innerHTML = "wwww ";