少了 tbody
tbody.appendChild(tr);
table.appendChild(tbody);
<body>
</body>
<script>
var obj =document.body
var tab =document.createElement("table")
tab.width="600"
tab.border=1;
tab.cellPadding=0;
tab.cellSpacing=0;
tab.align = "center";var tbd = document.createElement('tbody');
var tr=document.createElement("tr")
var td=document.createElement("td")
td.innerHTML="<strong>ID</strong>"
td.width="100"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>书名</strong>"
td.width="150"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>价格</strong>"
td.width="50"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>数量</strong>"
td.width="50"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>说明</strong>"
td.width="200"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>总价钱</strong>"
td.width="50"
tr.appendChild(td)tbd.appendChild(tr);
tab.appendChild(tbd)
obj.appendChild(tab)
</script>
tbody.appendChild(tr);
table.appendChild(tbody);
<body>
</body>
<script>
var obj =document.body
var tab =document.createElement("table")
tab.width="600"
tab.border=1;
tab.cellPadding=0;
tab.cellSpacing=0;
tab.align = "center";var tbd = document.createElement('tbody');
var tr=document.createElement("tr")
var td=document.createElement("td")
td.innerHTML="<strong>ID</strong>"
td.width="100"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>书名</strong>"
td.width="150"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>价格</strong>"
td.width="50"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>数量</strong>"
td.width="50"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>说明</strong>"
td.width="200"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>总价钱</strong>"
td.width="50"
tr.appendChild(td)tbd.appendChild(tr);
tab.appendChild(tbd)
obj.appendChild(tab)
</script>
<html>
<body>
</body>
<script>
var obj =document.body
var tab =document.createElement("table")
tab.width="600"
tab.border=1;
tab.cellPadding=0;
tab.cellSpacing=0;
tab.align = "center";
var oTbody = document.createElement("tbody");//放到Tbody里看看,没测试
var tr=document.createElement("tr")
var td=document.createElement("td")
td.innerHTML="<strong>ID</strong>"
td.width="100"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>?名</strong>"
td.width="150"
tr.appendChild(td)td=document.createElement("td")
td.innerHTML="<strong>价格</strong>"
td.width="50"
tr.appendChild(td)
alert("aa")
td=document.createElement("td")
td.innerHTML="<strong>数量</strong>"
td.width="50"
tr.appendChild(td)
alert("aa")
td=document.createElement("td")
td.innerHTML="<strong>?明</strong>"
td.width="200"
tr.appendChild(td)
alert("aa")
td=document.createElement("td")
td.innerHTML="<strong>?价?</strong>"
td.width="50"
tr.appendChild(td)
alert("aa")
oTbody.appendChild(tr);
tab.appendChild(oTbody);
document.body.appendChild(tab)
alert("a3")
</script>
</html>