I can understand the example below well, except: in the last click function, there is a .length property attached to `$(''.lightbulb.on')`. Im not sure how the .length property is working here. If someone could explain this for someone who is still very new to jQuery and javascript. Thanks.
`$('.lightbulb').on('changeState',function(e){
var light=$(this);
if(light.hasClass('on')){
light.trigger('turnOff');
}else{
light.trigger('turnOn')
}
}).on('turnOn',function(){
$(this).removeClass('off').addClass('on');
}).on('turnOff',function(){
$(this).removeClass('on').addClass('off');
});
$('.switch , .clapper').click(function(){
$(this).parent().find('.lightbulb').trigger('changeState');
});
$('#master_switch').click(function(){
if( $('.lightbulb.on').length ) {
$('.lightbulb').trigger('turnOff');
}else{
$('.lightbulb').trigger('turnOn');
}
});`