多个元素的jQuery选择器

Question

I know this isn't a code issue related question, but it's something I'd love to know and it may help others:

What's the difference between using this:

$(function() {
    var $fullArea = $('#full-sized-area');
    var $fullContent = $('#full-sized-content', $fullArea);
});

Over say this:

$(function() {
    var $fullArea = $('#full-sized-area');
    var $fullContent = $('#full-sized-content, #full-sized-area');
});

Answer 1

Both are quite difference.

Basically you are using Multiple Selector (“selector1, selector2, selectorN”) in the following line. So its simple

$('#full-sized-content, #full-sized-area')

Where as in line you are using context based selector, Here you are selecting element with ID full-sized-content in childs of $fullArea

var $fullContent = $('#full-sized-content', $fullArea); 

is equivalent to

var $fullContent = $('#full-sized-area').find('#full-sized-content');

Note As IDs must be unique in HTML you can simply use

var $fullContent = $('#full-sized-content');

Answer 2

There is a difference,

Demo : Multiple selector

var $fullContent = $('#full-sized-content, #full-sized-area');

Selects both the elements - Multiple selector : $('#elem1,#elem2,...')

---

Demo: Parent-child

var $fullContent = $('#full-sized-content', $fullArea);

In this case : #full-sized-content has to the child of #full-sized-area

So its is equivalent to

$('#full-sized-area #full-sized-content');
          Parent          Child                

Answer 3

Both are diffent here..

$(function() {
    var $fullArea = $('#full-sized-area');
    var $fullContent = $('#full-sized-content', $fullArea);
});

This one select element which has id "full-sized-content" under the #full-sized-area element

$(function() {
    var $fullArea = $('#full-sized-area');
    var $fullContent = $('#full-sized-content, #full-sized-area');
});

This one select both element with the ID full-sized-content and full-sized-area

Answer 4

var $fullContent = $('#full-sized-content', $fullArea);

The above actually a context based selector. So, what is does in simple manner is:-

$fullArea                           // get the fullArea element
    .find('#full-sized-content')    // find all the descendants with this id inside it

While the code below means:

// Get both the elements with id full-sized-content & full-sized-area
var $fullContent = $('#full-sized-content, #full-sized-area');

It's like a combined selector. So, if you do the below thing for 1st code:-

$fullContent.css('color', 'red');

It will only make the color red for the element #full-sized-content inside $fullArea Whereas if you use the same code for the 2nd part, it will color both the full-sized-content & full-sized-area elements.

FIDDLE DEMO

Answer 5

Your code:

var $fullContent = $('#full-sized-content', $fullArea);

it says find me #full-sized-content in $fullArea , because of the , . , makes a context for this.

---

This code:

var $fullContent = $('#full-sized-content, #full-sized-area');

is usually called a muliple selector selection which is a string with , separated elems while below

var $fullContent = $('#full-sized-content', $fullArea);

is usually finds an element in a given context which is , separated elems.