What is better, appending new elements via DOM functions, or appending strings with HTML tags?

Question

I have seen a few different methods to add elements to the DOM. The most prevelent seem to be, for example, either

document.getElementById(\'foo\').innerHTM         


        

Answer 1

According to this benchmark data, you will receive much faster results with innerHTML than creating DOM elements. It's especially clear when using older IE versions.

Answer 2

Some notes:

• Using innerHTML is faster in IE, but slower in chrome + firefox. Here's one benchmark showing this with a constantly varying set of <div>s + <p>s; here's a benchmark showing this for a constant, simple <table>.

• On the other hand, the DOM methods are the traditional standard -- innerHTML is standardized in HTML5 -- and allow you to retain references to the newly created elements, so that you can modify them later.

• Because innerHTML is fast (enough), concise, and easy to use, it's tempting to lean on it for every situation. But beware that using innerHTML detaches all existing DOM nodes from the document. Here's an example you can test on this page.

  First, let's create a function that lets us test whether a node is on the page:

  function contains(parent, descendant) {
      return Boolean(parent.compareDocumentPosition(descendant) & 16);
  }
  

  This will return true if parent contains descendant. Test it like this:

  var p = document.getElementById("portalLink")
  console.log(contains(document, p)); // true
  document.body.innerHTML += "<p>It's clobberin' time!</p>";
  console.log(contains(document, p)); // false
  p = document.getElementById("portalLink")
  console.log(contains(document, p)); // true
  

  This will print:

  true
  false
  true
  

  It may not look like our use of innerHTML should have affected our reference to the portalLink element, but it does. It needs to be retrieved again for proper use.

Answer 3

There are a number of differences:

1. innerHTML has only been standardised by the W3C for HTML 5; even though it has been a de facto standard for some time now across all popular browsers, technically in HTML 4 it's a vendor extension that standards-adherent developers would never be caught dead using. On the other hand, it's much more convenient and practically it's supported by all browsers.
2. innerHTML replaces the current content of the element (it does not let you modify it). But again, you gain in convenience if you don't mind this limitation.
3. innerHTML has been measured to be much faster (admittedly, that test involves older versions browsers that are not widely used today).
4. innerHTML might represent a security risk (XSS) if it's set to a user-supplied value that has not been properly encoded (e.g. el.innerHTML = '<script>...').

Based on the above, it seems that a practical conclusion might be:

• If you don't mind the fact that innerHTML is a bit limiting (only total replacement of DOM sub-tree rooted at target element) and you don't risk a vulnerability through injecting user-supplied content, use that. Otherwise, go with DOM.

Answer 4

First one is straight forward, easier to read, less code and might be faster.
Second one gives you much more control over the element you create, i.e. makes it much easier to modify the new Element using JS (like attaching events, or, just use it in your code).
Second way is for "purist" who like "clean" code (no quick and dirty).
I say, use both, see what fits you better and go with it.

Answer 5

I always prefer readability unless the perf difference is extreme. In a one-off case of this, it probably will be a marginal difference.

In a one-off case like this, setting the innerHTML property will be easiest to read.

But if you are doing a lot of programmatic content generation in JavaScript, it is cleaner and easier to read and understand the DOM option.

Example:

Compare this innerHTML code:

http://jsfiddle.net/P8m3K/1/

// Takes input of a value between 1 and 26, inclusive,
// and converts it to the appropriate character
function alphaToChar(alpha)
{
    return String.fromCharCode('a'.charCodeAt() + alpha - 1);
}

var content = "<ul>";
for(i = 0; i < 10; ++i)
{
    content += "<li>";
    for(j = 1; j <= 26; ++j)
    {
        content += "<a href=\"" + alphaToChar(j) + ".html\">"
            + alphaToChar(j)
            + "</a>";
    }
    content += "</li>";
}
document.getElementById("foo").innerHTML = content;

To this DOM code:

http://jsfiddle.net/q6GB8/1/

// Takes input of a value between 1 and 26, inclusive,
// and converts it to the appropriate character
function alphaToChar(alpha)
{
    return String.fromCharCode('a'.charCodeAt() + alpha - 1);
}

var list = document.createElement("ul");
for(i = 0; i < 10; ++i)
{
    var item = document.createElement("li");
    for(j = 1; j <= 26; ++j)
    {
        var link = document.createElement("a");
        link.setAttribute("href", alphaToChar(j) + ".html");
        link.innerText = alphaToChar(j);
        item.appendChild(link);
    }
    list.appendChild(item);
}
document.getElementById("foo").appendChild(list);

At this level they start to become quite similar length wise.

But the DOM code will be easier to maintain, and you're a bit less likely to make a typo or mistake that is hard to diagnose, like omitting a closing tag. Either your elements will be in your document, or they won't.

• With more complicated scenarios (like building treed menus), you'll probably come out ahead with DOM code.
• With scenarios where you have to append multiple types of content together to build a document with more heterogeneous content, it becomes a slam dunk. You don't have to ensure you call your child append code before calling the parent append code.
• With scenarios where add, remove, or modify existing static content, DOM will usually win.

If you start doing complicated DOM modifications (one of the last things I mentioned), you'll definitely want to check out a library built around DOM modifications, like jQuery.

Answer 6

Though this is an old thread, one thing that is not mentioned is the while innerHTML can be faster, care should be taken. Using innerHTML will render every child of the modified element, old and new alike. As such, one single innerHTML assignment is faster (slightly) than DOM create/append, but multiple innerHTML will definetly be slower.

For example:

for(let i=0; i < 10; i++)
   document.body.innerHTML+='<div>some text</div>';

will be nearly nearly 5x slower than

let html = '';
for(let i=0; i < 10; i++)
   html += '<div>some text</div>';

document.body.innerHTML = html;

Since innerHTML assignment is letting the browser natively create/append elements, the second methods results in 10 elements being natively created/appended, while the firstmethod results in 55 elements being created/appended (and 45 being destroyed): 1 element created on first loop-iteration, 2 elements created on the second loop-iteration (the original being destroyed), 3 elements created on the third loop-iteration (the previous 2 being destroyed), and so on.

If you use innerHTML for speed, you must make sure to create the entire html string first before making the innerHTML assignment, such as creating fresh DOM containers/elements. innerHTML, on the other hand, is a performance loser when appending any container with existing childNodes, especially those with large number of childNodes.