window.onload = function call() {

  function greatFunction(elem) {

//do stuff
}
         var textEditor1 = $('#cl1').find('textarea');
        textEditor1.on('focus change mousedown mouseout keyup mouseup', function () {
            greatFunction(this)
        });

        var textEditor2 = $('#cl2').find('textarea');
        textEditor2.on('focus change mousedown mouseout keyup mouseup', function () {
            greatFunction(this)
        });

        var textEditor3 = $('#cl3').find('textarea');
        textEditor3.on('focus change mousedown mouseout keyup mouseup', function () {
            greatFunction(this)
        });
}

<div id="cl1" class="cl active"><textarea id="chatTextarea" class="chatTextarea"></textarea></div>
<div id="cl2" class="cl"><textarea id="chatTextarea" class="chatTextarea"></textarea></div>
<div id="cl3" class="cl"><textarea id="chatTextarea" class="chatTextarea"></textarea></div>