A pop-up prompt for whether the search form submission is empty

Today I shared about judging whether the search form is empty. If it is empty, it will prompt that the search keyword is empty. The code is as follows:

  

<!--搜索表单-->
<script type="text/javascript">
    function notNull() {
        if (document.keyinput.kw.value.toString().trim().length <= 0) {
              alert("您未输入关键词！");
              document.keyinput.kw.focus();
              return false;
            }else {
              return true;
          }
     }
</script>
<div class="search clearfloat" id="search">
    <form method="get" action="http://www.zjkweiqi.cn/ search.php" class="search-form" name="keyinput">
    <input type="text" name="kw" placeholder="请输入商品/产品名，就能获取您需要的产品下载信息！"/>
        <button type="submit" onclick="return notNull()">搜一下</button>
    </form>
</div>
<!--搜索表单-->