required message not a alert in the javascript

Question

How can i write something a message not a alert when the input is empty.

Here in my code it is not preventing to submit the value when it is null, but how can i show a message like an required message that you need to insert something to search

if ( $( "#nameSearch" ).val().length === 0 ) {
    // some message that please insert something to search not an alert
    // required data-fv-notempty-message="This is required"
    event.preventDefault();
    } else {

Answer 1

<form method="post" onsubmit="return validate()">
<span class="error" id="name-error"></span>
<input type="text" name="nameSearch" id="nameSearch" >
<input type="submit" name="submit" value="submit" >
</form>

function validate()
{
    if ( $( "#nameSearch" ).val().length === 0 ) {
        $("#name-error").html("This is required");
        return false;
    } else {
        return true;
    }
}