<form onsubmit="return check();">
<input type="text" name="username">
<input type="submit" value="提交">
</form>
<script><form onsubmit="return check();">
<input<form onsubmit="return check();">
<input type="text" name="username">
<input type="submit" value="提交">
</form>
<script><form onsubmit="return check();">
<input