jsp 页面中比较输入的两个金额数

<script language="javascript">
function compare(){
var a1 = document.getElementById("amount").value;
var a2 = document.getElementById("amount2").value;
if(a1>a2){
alert("金额1不能>金额2");
}
}
</script>

<td>金额1
<input class="g_box" type="text" id="amount"
name="amount" maxlength="10"/>
</td><td>金额2
<input class="g_box" type="text" id="amount2"
name="amount2" maxlength="10" onBlur="compare();"/>
</td>