How to echo the variable in javascript which inside a function and store it in the php variable

Question

I have an html table and textboxes where on click on an row the row details get inserted in the textboxes all i want is to store those same values which are getting inserted into textboxes in a php variable so i can echo it or use the variable for someother purposes. How to print the f1.value in php. I want to store the f1.value in a variable and echo it in php so i can use it for my use case. i'm able to print through document.write, but i want to store the value in a php variable. f1.value changes dynamically as i click on a html table row.

(function () {
    if (window.addEventListener) {
        window.addEventListener('load', run, false);
    } else if (window.attachEvent) {
        window.attachEvent('onload', run);
    }

    function run() {
        var t = document.getElementById('myTable');
        t.onclick = function (event) {
            event = event || window.event; //IE8
            var target = event.target || event.srcElement;
            while (target && target.nodeName != 'TR') { // find TR
                target = target.parentElement;
            }
            //if (!target) { return; } //tr should be always found
            var cells = target.cells; 
            //var cells = target.getElementsByTagName('td'); //alternative
            if (!cells.length || target.parentNode.nodeName == 'THEAD') {
                return;
            }
            var f1 = document.getElementById('firstname');
            var f2 = document.getElementById('lastname');
            var f3 = document.getElementById('age');
            var f4 = document.getElementById('total');
            var f5 = document.getElementById('discount');
            var f6 = document.getElementById('diff');
            f1.value = cells[0].innerHTML;
            f2.value = cells[1].innerHTML;
            f3.value = cells[2].innerHTML;
            f4.value = cells[3].innerHTML;
            f5.value = cells[4].innerHTML;
            f6.value = cells[5].innerHTML;
   
   var df=f6.value;
   
  
   //document.write(f1.value);
   //document.write(f2.value);
   //document.write(f3.value);
   //document.write(f4.value);
   //document.write(f5.value);
   //document.write(df);
   
            //console.log(target.nodeName, event);
        };
    }

})();

<table id="myTable" cellspacing="1">
    <thead>
        <tr>
            <th>first name</th>
            <th>last name</th>
            <th>age</th>
            <th>total</th>
            <th>discount</th>
            <th>diff</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>peter</td>
            <td></td>parker
            <td></td>28
            <td></td>9.99
            <td></td>20.3%
            <td></td>+3
        </tr>
        <tr>
            <td>john</td>
            <td>hood</td>
            <td>33</td>
            <td>19.99</td>
            <td>25.1%</td>
            <td>-7</td>
        </tr>
        <tr>
            <td>clark</td>
            <td>kent</td>
            <td>18</td>
            <td>15.89</td>
            <td>44.2%</td>
            <td>-15</td>
        </tr>
        <tr>
            <td>bruce</td>
            <td>almighty</td>
            <td>45</td>
            <td>153.19</td>
            <td>44%</td>
            <td>+19</td>
        </tr>
        <tr>
            <td>bruce</td>
            <td>evans</td>
            <td>56</td>
            <td>153.19</td>
            <td>23%</td>
            <td>+9</td>
        </tr>
    </tbody>
</table>
Firstname is:
<input type="hidden" id="firstname" name="one" />
<br>Lastname is:
<input type="text" id="lastname" name="two"/>
<br>Age is:
<input type="text" id="age" />
<br>Total is:
<input type="text" id="total" />
<br>Discount is:
<input type="text" id="discount" />
<br>Diff is:
<input type="text" id="diff" />
</form>

Answer 1

You can't,

You want to store server side a client side var.

That's not possible