function initAcc(elem, option){
    //addEventListener on mouse click
    document.addEventListener('click', function (e) {
        //check is the right element clicked
        if (!e.target.matches(elem+' .a-btn')) return;
        else{
            //check if element contains active class
            if(!e.target.parentElement.classList.contains('active')){
                if(option==true){
                     //if option true remove active class from all other accordions 
                    var elementList = document.querySelectorAll(elem +' .a-container');
                    Array.prototype.forEach.call(elementList, function (e) {
                        e.classList.remove('active');
                    });
                }    
                //add active class on cliked accordion     
                e.target.parentElement.classList.add('active');
            }else{
                //remove active class on cliked accordion     
                e.target.parentElement.classList.remove('active');
            }
        }
    });
}
 
//activate accordion function
initAcc('.accordion', true);