fbJoinGroup

var mybtn = document.getElementsByClassName('_42ft _4jy0 _4jy3 _517h _51sy');
var i = 0;

var timer = setInterval(function() {
     if( i < mybtn.length) {
         mybtn[i].click();
         console.log("Click handler for button " + i + " fired");
     } else {
         clearInterval(timer);
     }
     i = i + 1;
}, 5000);