jQuery vs document.querySelectorAll

Question

document.querySelectorAll() has several inconsistencies across browsers and is not supported in older browsers^{This probably won't cause any trouble anymore nowadays}. It has a very unintuitive scoping mechanism and some other not so nice features. Also with javascript you have a harder time working with the result sets of these queries, which in many cases you might want to do. jQuery provides functions to work on them like: filter(), find(), children(), parent(), map(), not() and several more. Not to mention the jQuery ability to work with pseudo-class selectors.

However, I would not consider these things as jQuery's strongest features but other things like "working" on the dom (events, styling, animation & manipulation) in a crossbrowser compatible way or the ajax interface.

If you only want the selector engine from jQuery you can use the one jQuery itself is using: Sizzle That way you have the power of jQuerys Selector engine without the nasty overhead.

EDIT: Just for the record, I'm a huge vanilla JavaScript fan. Nonetheless it's a fact that you sometimes need 10 lines of JavaScript where you would write 1 line jQuery.

Of course you have to be disciplined to not write jQuery like this:

$('ul.first').find('.foo').css('background-color', 'red').end().find('.bar').css('background-color', 'green').end();

This is extremely hard to read, while the latter is pretty clear:

$('ul.first')
   .find('.foo')
      .css('background-color', 'red')
.end()
   .find('.bar')
      .css('background-color', 'green')
.end();

The equivalent JavaScript would be far more complex illustrated by the pseudocode above:

1) Find the element, consider taking all element or only the first.

// $('ul.first')
// taking querySelectorAll has to be considered
var e = document.querySelector("ul.first");

2) Iterate over the array of child nodes via some (possibly nested or recursive) loops and check the class (classlist not available in all browsers!)

//.find('.foo')
for (var i = 0;i<e.length;i++){
     // older browser don't have element.classList -> even more complex
     e[i].children.classList.contains('foo');
     // do some more magic stuff here
}

3) apply the css style

// .css('background-color', 'green')
// note different notation
element.style.backgroundColor = "green" // or
element.style["background-color"] = "green"

This code would be at least two times as much lines of code you write with jQuery. Also you would have to consider cross-browser issues which will compromise the severe speed advantage (besides from the reliability) of the native code.

If you are optimizing your page for IE8 or newer, you should really consider whether you need jquery or not. Modern browsers have many assets natively which jquery provides.

If you care for performance, you can have incredible performance benefits (2-10 faster) using native javascript: http://jsperf.com/jquery-vs-native-selector-and-element-style/2

I transformed a div-tagcloud from jquery to native javascript (IE8+ compatible), the results are impressive. 4 times faster with just a little overhead.

                    Number of lines       Execution Time                       
Jquery version :        340                    155ms
Native version :        370                    27ms

You Might Not Need Jquery provides a really nice overview, which native methods replace for which browser version.

http://youmightnotneedjquery.com/

---

Appendix: Further speed comparisons how native methods compete to jquery

• Array: $.inArray vs Array.indexOf: Jquery 24% slower

• DOM: $.empty vs Node.innerHtml: Jquery 97% slower

• DOM: $.on vs Node.addEventListener: Jquery 90% slower

• DOM: $.find vs Node.queryselectorall: Jquery 90% slower

• Array: $.grep vs Array.filter: Native 70% slower

• DOM: $.show/hide vs display none: Jquery 85% slower

• AJAX: $.ajax vs XMLHttpRequest: Jquery 89% slower

• Height: $.outerHeight vs offsetHeight: Jquery 87% slower

• Attr: $.attr vs setAttribute: Jquery 86% slower

To understand why jQuery is so popular, it's important to understand where we're coming from!

About a decade ago, top browsers were IE6, Netscape 8 and Firefox 1.5. Back in those days, there were little cross-browser ways to select an element from the DOM besides Document.getElementById().

So, when jQuery was released back in 2006, it was pretty revolutionary. Back then, jQuery set the standard for how to easily select / change HTML elements and trigger events, because its flexibility and browser support were unprecedented.

Now, more than a decade later, a lot of features that made jQuery so popular have become included in the javaScript standard:

• Instead of jQuery's $(), you can now now use Document.querySelectorAll()
• Instead of jQuery's $el.on(), you can now use EventTarget.addEventListener()
• Instead of jQuery's $el.toggleClass(), you can now use Element.classList.toggle()
• ...

These weren't generally available back in 2005. The fact that they are today obviously begs the question of why we should use jQuery at all. And indeed, people are increasingly wondering whether we should use jQuery at all.

So, if you think you understand JavaScript well enough to do without jQuery, please do! Don't feel forced to use jQuery, just because so many others are doing it!

That's because jQuery can do much more than querySelectorAll.

First of all, jQuery (and Sizzle, in particular), works for older browsers like IE7-8 that doesn't support CSS2.1-3 selectors.

Plus, Sizzle (which is the selector engine behind jQuery) offers you a lot of more advanced selector instruments, like the :selected pseudo-class, an advanced :not() selector, a more complex syntax like in $("> .children") and so on.

And it does it cross-browsers, flawlessly, offering all that jQuery can offer (plugins and APIs).

Yes, if you think you can rely on simple class and id selectors, jQuery is too much for you, and you'd be paying an exaggerated pay-off. But if you don't, and want to take advantage of all jQuery goodness, then use it.

jQuery's Sizzle selector engine can use querySelectorAll if it's available. It also smooths out inconsistencies between browsers to achieve uniform results. If you don't want to use all of jQuery, you could just use Sizzle separately. This is a pretty fundamental wheel to invent.

Here's some cherry-pickings from the source that show the kind of things jQuery(w/ Sizzle) sorts out for you:

Safari quirks mode:

if ( document.querySelectorAll ) {
  (function(){
    var oldSizzle = Sizzle,
      div = document.createElement("div"),
      id = "__sizzle__";

    div.innerHTML = "<p class='TEST'></p>";

    // Safari can't handle uppercase or unicode characters when
    // in quirks mode.
    if ( div.querySelectorAll && div.querySelectorAll(".TEST").length === 0 ) {
      return;
    }

If that guard fails it uses it's a version of Sizzle that isn't enhanced with querySelectorAll. Further down there are specific handles for inconsistencies in IE, Opera, and the Blackberry browser.

  // Check parentNode to catch when Blackberry 4.6 returns
  // nodes that are no longer in the document #6963
  if ( elem && elem.parentNode ) {
    // Handle the case where IE and Opera return items
    // by name instead of ID
    if ( elem.id === match[3] ) {
      return makeArray( [ elem ], extra );
    }

  } else {
    return makeArray( [], extra );
  }

And if all else fails it will return the result of oldSizzle(query, context, extra, seed).