How to assign elem.value from JS to a variable in php?

Question

PHP

there is such a function in the script

function plus() {
...
    input.value = parseInt(input.value) + 1;
...
}

Adds +1 to elem.value on button click.
How to assign "input.value" to a variable in php for further sending to the mail?
Something like
$var= $_POST['input.value'];

Answer 1

use ajax and when increasing the value, send a request with the value, and already in php process and send