JavaScript: Is it better to use innerHTML or (lots of) createElement calls to add a complex div structure? [duplicate]

I'm looking at a problem that needs a complex block of divs to be created once for each element in a set of ~100 elements.

Each individual element is identical except for the content, and they look (in HTML) something like this:

<div class="class0 class1 class3">
<div class="spacer"></div>
<div id="content">content</div>
<div class="spacer"></div>
<div id="content2">content2</div>
<div class="class4">content3</div>
<div class="spacer"></div>
<div id="footer">content3</div>
</div>

I could either:

1) Create all the elements as innerHTML with string concatenation to add the content.

2) Use createElement, setAttribute and appendChild to create and add each div.

Option 1 gets a slightly smaller file to download, but option 2 seems to be slightly faster to render.

Other than performance is there a good reason to go via one route or the other? Any cross-browser problems / performance gremlins I should test for?

...or should I try the template and clone approach?

Many thanks.

Solution 1:

Neither. Use a library like jQuery, Prototype, Dojo or mooTools because both of these methods are fraught with trouble:

Did you know that innerHTML on tables for IE is readonly?
Did you know for the select element it's broken as well?
How about problems with createElement?

The writers of the major javascript libraries have spent a lot of time and have entire bug tracking systems to make sure that when you call their DOM modifying tools they actually work.

If you're writing a library to compete with the above tools (and good luck to you if you are), then I'd choose the method based on performance, and innerHTML has always won out in the past, and since innerHTML is a native method, it's a safe bet it will remain the fastest.

Solution 2:

Depends on what's "better" for you.

Performance

From a performance point of view, createElement+appendChild wins by a LOT. Take a look at this jsPerf I created when I compare both and the results hit in the face.

innerHTML: ~120 ops/sec
createElement+appendChild: ~145000 ops/sec

(on my Mac with Chrome 21)

Also, innerHTML triggers page reflow.

On Ubuntu with Chrome 39 tests get similar results

innerHTML: 120000 ops/sec
createElement: 124000 ops/sec

probably some optimisation take place. On Ubuntu with QtWebkit based browser Arora (wkhtml also QtWebkit) results are

innerHTML: 71000 ops/sec
createElement: 282000 ops/sec

it seems createElement faster in average

Mantainability

From a mantainability point of view, I believe string templates help you a lot. I use either Handlebars (which I love) or Tim (for project which need smallest footprints). When you "compile" (prepare) your template and it's ready for appending it to the DOM, you use innerHTML to append the template string to the DOM. On trick I do to avoid reflow is createElement for a wrapper and in that wrapper element, put the template with innerHTML. I'm still looking for a good way to avoid innerHTML at all.

Compatibility

You don't have to worry here, both methods are fully supported by a broad range of browsers (unlike altCognito says). You can check compatibility charts for createElement and appendChild.

Solution 3:

altCognito makes a good point - using a library is the way to go. But if was doing it by hand, I would use option #2 - create elements with DOM methods. They are a bit ugly, but you can make an element factory function that hides the ugliness. Concatenating strings of HTML is ugly also, but more likely to have security problems, especially with XSS.

I would definitely not append the new nodes individually, though. I would use a DOM DocumentFragment. Appending nodes to a documentFragment is much faster than inserting them into the live page. When you're done building your fragment it just gets inserted all at once.

John Resig explains it much better than I could, but basically you just say:

var frag = document.createDocumentFragment();
frag.appendChild(myFirstNewElement);
frag.appendChild(mySecondNewElement);
...etc.
document.getElementById('insert_here').appendChild(frag);