........这段代码怎样写啊?______（文本框内容检测）

1<script language="javascript">   
2function check(theform)   
3{ 这里应该怎样写啊？}   
4</script>

1<form method="post" name="theform">
2<input name="text" type="text"/>
3<input name="submit" onclick="check(this)" type="submit" value="submit"/>
4</form>

 1<script language="javascript">   
 2function check()   
 3{   
 4if(!/[a-zA-Z0-9]/g.test(theform.text.value)){   
 5alert('输入不符合要求')   
 6return false   
 7}   
 8return true   
 9}   
10</script>

1<form method="post" name="theform">
2<input name="text" type="text"/>
3<input name="submit" onclick="return check()" type="submit" value="submit"/>
4</form>