JSFiddle - React, Tailwind, and code Playground

HTML

<div class="elem1"></div>
<div class="elem1"></div>
<div class="elem1"></div>
<div class="elem2"></div>
<div class="elem2"></div>
<div class="elem2"></div>
<div class="elem3"></div>
<div class="elem3"></div>
<div class="elem3"></div>

<input type="button" id="getSelectorInfo" value="Test" />

JavaScript

var counterElemTested=0;
$.extend($.expr[':'],{
    mySelector:function(){
        ++counterElemTested;
    }
});

$('#getSelectorInfo').click(function(){
    $('.elem1:mySelector(true)');
    alert('counterElemTested:'+counterElemTested);
    counterElemTested=0;
});

//Chrome -> counterElemTested=3
//Ie7,8 (didn't check Ie6,9) -> counterElemTested=24 !