trying to understand. I have a js code,

 $(document).on('click','.plan_btn',function() {
        $('.ui-dropdown').removeClass('active');
        var tarifplanid=$(this).attr('data-tarifplanid');
        $('.planid').text(tarifplanid);
            $('.add_plan').addClass('show');
        });

I have a php code, with button, where I pass attr.

<button type="button" class="ui-component ui-button plan_btn" data-tarifplanid="<?php echo($plan->plan_id)?>">Select</button>

So, by pressing Select button, I will have an planID, which is 2 or 3 stored in .JS

Then, as test, I have the following code:

 <?php
    $test = <<<EOD
    <span class="planid"></span>
    EOD;
echo $test;?>

Question is:

1. echo returns ID, 2 or 3, depends on which item I pressed "Select"
2. But, when I trying to add a link with $test, it will as <span class="planid"></span>

Why? I assume it should be https://localhost/2 but I have https://localhost/<span class="planid"></span>

Thank you! I'm not a developer, just browsing and a learning a bit