javascript-onsubmit触发事件把表单数据发送到相关php处理问题

问题详情：onsubmit触发事件把表单数据发送到相关php处理但是如何避免数据有问题时也会触发事件呢？

if(isset($_POST['submit'])){ //第10行

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$name=$_POST['name'];
$score=$_POST['score'];
$st=$_FILES['st']['name'];
$st_type=$_FILES['st']['type'];
$st_size=$_FILES['st']['size'];
$output_form=false;

if( empty($name) || empty($score) || empty($st))
{
echo'Something is wrong !
';
$output_form=true;
}
//第20行
else{

if( (($st_type=='image/gif')||($st_type=='image/jpeg')||($st_type=='image/pjeg')||($st_type=='image/png')) && ($st_size >0) && ($st_size {

if($_FILES['st']['error']==0){

$target=GW_UPLOADPATH .$st;
//第30行

if(move_uploaded_file($_FILES['st']['tmp_name'],$target)){

$dbc=mysqli_connect(HOST,USER,PASSWORD,NAME);

$st=$_FILES['st']['name'];
$query="INSERT INTO b (date,st,score,name)".
"VALUES(NOW(),'$st','$score','$name')";
//第40行

mysqli_query($dbc,$query)
or die('UU');

echo'You are success to add dates to Mysql '.'<br>';echo 'Name :'.$name.'<br>';echo 'Score : '.$score.'<br>';echo 'Photo :'.'@@##@@';                //第50行          echo'<p><a href="index.php">Back to index page</a></p>';

//clear the score datas
$name="";
$score="";
$st="";

mysqli_close($dbc);

}//if(move_uploaded_f

else
{
echo $_FILES['st']['error'];
echo'
文件没有移动成功 ！！';//第60行

}

}//if($_FILES['st']['error']

else
echo'There is something wrong to upload the file ! Plese upload it agian.';

}//if(($st_type=='image/gif'

else echo'

The screen pic must be a GIF,JPEG, or PNG image and the file '.'size must fit '.'(MAX_FILE_SIZE/1024)'.'KB.

}//else                //第70行

//Try to delete the temporary screen shot image file.

@unlink($_FILES['st']['tmp_name']);

}else $output_form=true;

if($output_form){
?>