javascript how to create a validation error message without using alert

I am looking to make a simple form validation error message that displays under the username field.

I cannot seem to figure it out.

<form name ="myform" onsubmit="validation()">
     Username: <input type ="text" name="username" /><br />              
     <input type ="submit" value="submit" />
      <div id ="errors">
      </div>
</form>

Here is my validation script:

function validation(){ 
    if(document.myform.username.value == ""){   //checking if the form is empty
         document.getElementById('errors').innerHTML="*Please enter a username*";
                //displaying a message if the form is empty
    }