title: how to check if input field is empty on submit
body: <p>I'm using jQuery so i wonder how can i show error message after i click submit button only if an input field is empty.</p>
  
  <p>Below the code my simple form how to apply to it.</p>
  
  <pre><code>&lt;form id="myid" name="myid" method="post" action="hook.php"&gt;
  
  name : &lt;input type="text" name="name" id="name"&gt;
  
  age : &lt;input type="text" name="age" id="age"&gt;
  
  &lt;input type="submit" id="submit" name="submit" value="Save" /&gt;
  
  &lt;/form&gt;
  </code></pre>
  
  <p>I would like to show error like this</p>
  
  <p><img src="https://i.stack.imgur.com/JMCD5.png" alt="enter image description here"></p>