Code to process the data and then submit the form

The content introduced below is applicable when the form information on the front-end page is not filled in before submitting or saving.

When the information is empty, generally we must not submit the form to The database should prompt that the information is not filled in or empty. This step can be completed by the front end or the back end. However, in order to reduce the burden on the server, it is recommended that the front end complete the judgment.

function check(){
   var name = document.getElementById("name").value;   
   if(name ==  null || name == ''){
        alert("用户名不能为空");
        return false;
   }
   return true;
}

<form name="mainform" action="form.php" method="post"  onsubmit="return check()">
  <input type="text" id="name"/>
  <input type="sumit" value="提交"/>
</form>

onsubmit="return check() "The return in " must be added, otherwise even if the return value of check is false, it will still be submitted. In other words, onsubmit="return false" does not execute submission; onsubmit="return true" or onsubmit="return" both execute submission.

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