php-coding/5.work2.idv.php

<?php
$id_number = trim($_POST['id_number']);
if(strlen($id_number)!=18){
    echo <<<eol
<script>
alert("提交的身份证号长度不正确,请重新提交");
history.back();
</script>
eol;
}
else{
    echo "提交的身份证号长度正确";
}