How to create php object from within javascript [duplicate]

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I want to instantiate a php object from javascript on keyup event.I am using ajax to make a live search system, when the the search field is empty i want to run a php function/instantiate object that displays ALL items again. This can only be done by checking keyup event in javascript.

Tried calling the object from jquery .html() function no success

//on click

function dontShowSearches() {
    $("#tour_container").html(
        "<?php $tour = new Tours; $tour->Display_tours($con);?>
        ");
    }