this.offset is not a function within a click function

Question

The error is that _this.offset is not a function. I logged this to the console and it was the <li> element I clicked on, so I am confused why this would not work.

$('.item').click(function(e) {
  var _this = this;
  var topx = _this.offset().top;
  var leftx = _this.offset().left;
  var moveArea = $('#replace').offset().top;
  var moveLeft = $('#replace').offset().left;
  var moveUp = topx - moveArea - 50;
  _this.css('position', 'absolute').css('top', moveUp).css('zIndex', 50).css('left', leftx);
  _this.animate({
    top: -50,
    left: moveLeft
  }, 300)
});

#replace {
  height: 50px;
  width: 100px;
  background-color: green;
}

#list {
  height: 200px;
  overflow-y: scroll;
}

.item {
  height: 50px;
  width: 100px;
  background-color: blue;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.2/jquery.min.js"></script>
<div id="replace">
  Replace this
</div>

<ul id="list">
  <li class="item">TEST</li>
  <li class="item">TEST</li>
  <li class="item">TEST</li>
</ul>

I also want to create an animation such that the item I click in the list moves up to replace the green "Replace this" box, if someone could help with that too.

I created a jsfiddle to show the error: https://jsfiddle.net/v5fjjwmj/2/

Answer 1

this (and hence _this) inside your event handler refers to a DOMElement which doesn't have the offset() method as that's part of jQuery. To fix this you can create a jQuery object using $(this):

$('.item').click(function(e) {
    var $this = $(this);
    var topx = $this.offset().top;
    var leftx = $this.offset().left;
    var moveArea = $('#replace').offset().top;
    var moveLeft = $('#replace').offset().left;
    var moveUp = topx - moveArea - 50;

    $this.css({
        'position': 'absolute',
        'top': moveUp,
        'zIndex': 50,
        'left': leftx
    }).animate({
        top: -50,
        left: moveLeft
    }, 300)
});

Also note the use of the object provided to a single css() call over multiple calls to the same method.

Answer 2

Replace these two lines:

var topx = _this.offset().top;
var leftx = _this.offset().left;

with:

var topx = _this.offsetTop;
var leftx = _this.offsetLeft;

As .offset() is a jquery function and _this is a DOM element.

---

Also for your .css line you have to wrap _this in $(...) again because _this is a DOM element and **not a jQuery object.