FAQ: Mouse Events - currentTarget


#1

This community-built FAQ covers the “currentTarget” exercise from the lesson “Mouse Events”.

Paths and Courses
This exercise can be found in the following Codecademy content:

Web Development

Introduction to jQuery

FAQs on the exercise currentTarget

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#2

Instead of using an arrow function with an event parameter that calls upon event.currentTarget, couldn’t I instead write a function that uses $(this)? They both seem to work, but is one preferred over another?

  $('.product-photo').on('mouseenter', event => {
    $(event.currentTarget).addClass('photo-active')
  }).on('mouseleave', event => {
    $(event.currentTarget).removeClass('photo-active')
  })
  $('.product-photo').on('mouseenter', function () {
    $(this).addClass('photo-active');
  }).on('mouseleave', function () {
    $(this).removeClass('photo-active');
  })

#3

An author may prefer one over the other but there is no industry standard that says we need to choose one over the other (that I am aware of). It’s possible the lesson author was presenting this as the alternative approach. We know that arrow functions do have this locally so the only means of accessing the event object is through the parameter, which has a currentTarget attribute we can poll.

Bottom line, write with consistency, meaning use one approach or the other, not both as this will only help to confuse things.


#4

Is it neccesary to use th event parameter

When I use

  $('.product-photo').on('mouseenter', () => {
    $(event.currentTarget).addClass('photo-active')
  }).on('mouseleave', () => {
    $(event.currentTarget).removeClass('photo-active')
  })

instead of

  $('.product-photo').on('mouseenter', event => {
    $(event.currentTarget).addClass('photo-active')
  }).on('mouseleave', event => {
    $(event.currentTarget).removeClass('photo-active')
  })

this works fine.

Is there any reason to use event as a parameter?


#5

Yes, to give context to the event. What we call the variable is arbitrary, but we do need it in the parameter. Without it, the handler will not work.

With every event that is triggered, JS creates an EventObject and gives it the name we supply in the parameter, whether we use event or e or anything else.

If we poll the event object we will find it has a currentTarget attribute that references the DOM node upon which the event takes place.


#6

Ok, what do you exactly mean with

Without it, the handler will not work.

because if I don’t use it in my code everything seems to work

example:

 $('.product-photo').on('mouseenter', () => {
    $(event.currentTarget).addClass('photo-active')
  }).on('mouseleave', () => {
    $(event.currentTarget).removeClass('photo-active')
  })

#7

It’s unfortunate the old jQuery track has been removed. I’ve searched everywhere and cannot find the demonstration I did on the EventObject. That was years ago and long ago forgotten, and without the Mario lesson, I’m afraid it’s lost.

In jQuery, event is an attribute so you may wish to ignore the part about using any variable. event is the one to use.

The shoe image should zoom in slightly on mouseover, and restore on mouseout. When I run your code it does not work, but it works perfectly when event is used as parameter.


#8

that’s strange. for me it works. The shoe image should zoom in slightly on mouseover, and restore on mouseout.

I just use () => instead of event =>

I have also done this in other exercises and it always seems to work…


#9

It could be the browser that is automatically sharing the event object with the handler, but we should never make the assumption that it works in all environments. Use the parameter for a safer bet.

The event object is guaranteed to be passed to the event handler.
https://api.jquery.com/category/events/event-object/

Just what that means will take some further research. My jQuery is rusty from lack of use. See if you can find how to expose all the attributes and methods of the event object.

$(event.initialObject).each(function (x) { console.log(x); })

Can’t say that will work. It would need to be inside the handler to capture the actual event. May have to break out of the CC environment and try this at home.

There are attributes and methods, so one may wish to print out only the attributes, and not anything that is type function.

With some more digging through old bookmarks in my other browser I found this topic…

https://www.codecademy.com/forum_questions/556076b8d3292fb209000260

It explores the keyup event, but the object will be similar for any event.


Here is that code in case the URL becomes unreachable…

$(document).ready(function() {
    $(document).keyup(function(e) {
        var str='';
        for (var k in e){
            if (typeof e[k] !== 'function'){
                str += k.toString()+": "+e[k]+"<br>"
            }
        }
        $('p').html(str);
        switch(parseInt(e.which,10)) {
            case 37: //left
            $('img').animate({left: "-=10px"},'fast');
                break;
            case 38: //up
            $('img').animate({top: "-=10px"},'fast');     
                break;
            case 39: //right
            $('img').animate({left: "+=10px"},'fast');  
                break;
            case 40: //down
            $('img').animate({top: "+=10px"},'fast');    
                break;
        }
    });
});

Before running, add an empty

to index.html, just above the tag.

What you are reading is the property list of the KeyboardEventObject (minus the functions, which have been filtered out). Note that in this example I used e, not key. There is no connection to the key: property so don’t let that throw you off.