<form name="form1" method="post" action="" onSubmit="return false;">
<input name="S" type="text" id="S">
<input type="submit" name="Submit" onclick="alert(S.value.substring(1,2))" value="提交">
</form>
<input name="S" type="text" id="S">
<input type="submit" name="Submit" onclick="alert(S.value.substring(1,2))" value="提交">
</form>
<input type="submit" name="Submit" onclick="alert(str.value.substr(1,1))" value="提交">