Display “Name” in case url parameters are absent

Question

I am not sure whether this is right, but I request for your help where possible.

Below is my code. It displays the url parameters but in case of no parameters, its blank insted of displaying "Name"

<script>  
{
    var str = document.getElementById("id1").innerHTML; 
    var res = str.replace(/Name/gi, "<?php echo $_GET['n'];  ?>");    
    document.getElementById("demo").innerHTML = res;
}
</script>

<p id="id1">Name</p>

Answer 1

Because you are changing all the HTML inside the demo id tag.

<div id="demo"> Name</div>

If res = 'My';

document.getElementById("demo").innerHTML = res;

Result

<div id="demo">My</div>

Above line will overide any data inside id demo element with you definded HTML.

Answer 2

You only need to replace it if the query parameter exists. If not, just use the original:

var str = document.getElementById("id1").innerHTML; 

<?php if (isset($_GET['n'])) : ?>
    str = str.replace(/Name/gi, "<?= $_GET['n'] ?>");
<?php endif ?>

document.getElementById("demo").innerHTML = str;