How can I get the ID of an element using jQuery?

Above answers are great, but as jquery evolves.. so you can also do:

var myId = $("#test").prop("id");

The jQuery way:

$('#test').attr('id')

In your example:

$(document).ready(function() {
  console.log($('#test').attr('id'));
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="test"></div>

Or through the DOM:

$('#test').get(0).id;

or even :

$('#test')[0].id;

and reason behind usage of $('#test').get(0) in JQuery or even $('#test')[0] is that $('#test') is a JQuery selector and returns an array() of results not a single element by its default functionality

an alternative for DOM selector in jquery is

$('#test').prop('id')

which is different from .attr() and $('#test').prop('foo') grabs the specified DOM foo property, while $('#test').attr('foo') grabs the specified HTML foo attribute and you can find more details about differences here.

$('selector').attr('id') will return the id of the first matched element. Reference.

If your matched set contains more than one element, you can use the conventional .each iterator to return an array containing each of the ids:

var retval = []
$('selector').each(function(){
  retval.push($(this).attr('id'))
})
return retval

Or, if you're willing to get a little grittier, you can avoid the wrapper and use the .map shortcut.

return $('.selector').map(function(index,dom){return dom.id})

id is a property of an html Element. However, when you write $("#something"), it returns a jQuery object that wraps the matching DOM element(s). To get the first matching DOM element back, call get(0)

$("#test").get(0)

On this native element, you can call id, or any other native DOM property or function.

$("#test").get(0).id

That's the reason why id isn't working in your code.

Alternatively, use jQuery's attr method as other answers suggest to get the id attribute of the first matching element.

$("#test").attr("id")