What does "this" word do in jQuery?

Question

So, here is the question

I can not undestand when i should use "this" instead class or id

If u can show example - it will be fantastic

Thanks

Answer 1

I can not undestand when i should use "this" instead class or id

Usually, you do that when you want to refer to the element on which an event was triggered from within the event handler:

$(".foo").on("click", function() {
    var $el = $(this);           // `this` is the element that was clicked,
                                 // so `$(this)` gives you a jQuery wrapper
                                 // around just that one element.
                                 // But $(".foo") would give you a wrapper
                                 // around **all** .foo elements, not just the
                                 // one that was clicked.
    // ...
});

Live Example:

$(".foo").on("click", function() {
  var $el = $(this); // `this` is the element that was clicked
  $el.text("You've clicked this one");
});

<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<div class="foo">Not clicked yet</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

Sometimes, it comes up when using either each or $.each, because jQuery calls the callback to each of those methods with this referring to the element for that call:

$(".foo").each(function() {
    var $el = $(this);               // `this` is the element for this callback
    // ...
});

The jQuery API documentation will tell you when it's going to set this to a specific value in a callback.