了解jQuery $（this）.closest（element）;

Question

I would just like to know what $(this) refers to when you use it within a function called by a button.

Is it referring to the button element or is it referring to the function itself.

Code example:

<div>
<span class="fileError"></span>
<input type="file" class="understanding" />
</div>

<script>
$('.understanding').click(function(){

   $(this).closest('div').find('span.fileError').html('My brain needs help');
});
</script>

Things I have tried to change the html of my span

$(this).prev('span.fileError').html();

$(this).closest('div').find('span.fileError').html();

$(this).closest('div').find('span.fileError').text();

Links I have tried:

Jquery:find input field closest to button

Understand javascripts 'this' with clarity

Finding Closest p tag to the clicked button

I have look at more places, thought I would just show those I found most informing. What do I need to do here and to what $(this) is referring within the function?

Answer 1

Is it referring to the button element or is it referring to the function itself.

In jQuery event handler functions, this refers to the DOM element itself, and $(this) wraps that in a jQuery object.

But the real answer to your question of how to change the HTML of your span is going to depend on what fileupload is.

Answer 2

It depends on what kind of function will you use as event handler:

• arrow function takes this from the outer scope
• normal function has this assigned to a current element when used as an event handler.

 $('.understanding-arrow').click(() => { console.log(this === window && "this is window"); $(this).closest('div').find('span.fileError').html('My brain needs help'); }); $('.understanding-normal').click(function() { console.log(this === $('.understanding-normal')[0] && "this is input el"); $(this).closest('div').find('span.fileError').html('My brain needs help'); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div> <span class="fileError"></span> <input type="button" class="understanding-arrow" value="arrow function" /> </div> <div> <span class="fileError"></span> <input type="button" class="understanding-normal" value="normal function" /> </div>