Asynchronous JavaScript; Using JavaScript to Insert JavaScript

Xah Lee, 2010-10-30, 2011-10-09

This page shows you how to use JavaScript (js) to insert a HTML that contains js code and have that js code run. If you don't know how to insert a element using js, see: Adding HTML Content with JavaScript.

The Problem

There are lots JavaScript based widgets today. For example, web share widget ◇ Google search widget ◇ Comment widget ◇ twitter ◇ facebook ◇ amazon ads… etc. They let you easily add functionality to your site.

If your webpage is static HTML, or generated by PHP or content manager software, you can directly include these widgets at the right place at the server side. However, sometimes it is convenient to use a js to insert them. Because, you may want the location of the widget to be different for different pages. Or, only centain pages you want to include the widget, but you don't know which until the page is generated.

So, the solution is to use a client side js that insert these js based widgets.

If you use a JavaScript to insert a js code xyz, will the newly inserted xyz script run?

Using innerHTML Does Not Work

First, let's see what happens if you don't do anything special.

Suppose you want to use js to insert the following js code.

<div class="xyz">
 <p>Fantastic!</p>
 <script>alert("woot!");</script>
</div>

Suppose you do it this way:

var myElement = document.createElement("div"); // create new div element

myElement.setAttribute("class", "xyz"); // add a class attribute

// add HTML in the div element
myElement.innerHTML='<p>Fantastic!<\/p> <script>alert("woot!");<\/script>';

// add the new element after the first p tag
document.body.insertBefore(myElement, (document.getElementsByTagName("p"))[0]);

It will fail in IE8, Google Chrome, Opera. (but works in Firefox 3.6.12).

You can see what your browser do here: js_insert_js.html.

Creating Script Object by createElement

Here's how to make it work. It's easy. Instead of using myElement.innerHTML="<script>…</script>";, you should create the “script” element as a DOM object, then you insert this object.

Here's a sample JavaScript code:

var ele = document.createElement("script");
ele.type = "text/javascript";
ele.innerHTML = 'alert("woot!")';

document.body.insertBefore(ele, (document.getElementsByTagName("p"))[0]);

Here's a test page using this code: test page: Using JavaScript to Insert JavaScript.

Twitter Example

Suppose you want to insert this code:

<div class="twtr">
<a href="http://twitter.com/share" class="twitter-share-button" data-count="vertical" data-via="xah_lee">Tweet</a>
<script type="text/javascript" src="http://platform.twitter.com/widgets.js"></script>
</div>

It's a widget that shows a Twitter button with number of tweets of the page.

Here's how you do it in your js:

// insert a twitter div tag before element “cg”
function insertTwitter (cg) {
    var mdv = document.createElement("div");
    mdv.setAttribute("class", "twt");

    mdv.innerHTML='<a href="http://twitter.com/share" class="twitter-share-button" data-count="vertical" data-via="xah_lee">Tweet</a>';

    var ele = document.createElement("script");
    ele.type = "text/javascript";
    ele.src = "http://platform.twitter.com/widgets.js";

    mdv.appendChild(ele);

    document.body.insertBefore(mdv, cg);

}

// insert before the first p tag
insertTwitter((document.getElementsByTagName("p"))[0]);

Thanks to “idealmachine” and DVK. Source stackoverflow.com.