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Metamorph.js is a library that allows you to create a string of HTML, insert it into the DOM, and update the contents later. It works for normal cases, like inserting text into a <p> tag, and more complicated cases, like updating an <li> inside a <ul> or a <tr> inside a <table> (even after the <tbody> was automatically generated).

The motivation for the Metamorph library is to make it possible for template engines to insert arbitrary content into a String of outputted HTML that they are generating with the ability to replace exactly that content later.

Supported Browsers

Metamorph.js works on all browsers that support the W3C range API, with a pure-DOM-based fallback for browsers that don't. Since virtually all browsers except for Internet Explorer support the W3C range API, the DOM-based fallback was developed and tested using Internet Explorer.

It has been tested on Internet Explorer 6+, Firefox 3+, Safari 5, and the current version of Chrome.

It should work on virtually all browsers currently in wide use. If you find that the tests don't run on a generally available browser, please file a bug.


// create the morph object
var morph = Metamorph("HI!");

// insert it into the DOM

// replace the contents

// remove the morph

// append the morph to an existing element, useful when
// manually creating morphs and not using a templating library


Metamorph.js does not insert any visible, stylable elements into the DOM and does not modify the DOM depth of the contents. This means that existing stylesheets should work without modification.

When working with elements with particular content models, such as tables, you may insert any valid content. For example, you may insert a <tr> or <tbody> into a <table>, but not other content. You may insert an <li> into a <ul>, but not a <p>.

This holds for the initial insertion as well as any updates.

var ul = $("<ul>").appendTo("body").end();

var morph = Metamorph("<li>HI!</li>");
ul.append(morph.outerHTML()); // legal

var otherMorph = Metamorph("<p>HI!</p>");
ul.append(otherMorph.outerHTML()); // illegal

morph.html("<li>BYE!</li>") // legal
morph.html("<p>BYE!</p>") // illegal


Metamorph.js inserts a starting and ending <script> tag in the outerHTML of a morph object. In all browsers, <script> tags may appear anywhere in the DOM and do not affect display.

In browsers that support W3C ranges, the implementation is rather straight forward. Metamorph.js creates a range, and places its starting point after the first placeholder, and its ending point before the second placeholder. It then deletes the contents of the range.

Then, using range.createContextualFragment, it creates a document fragment for the content and inserts it into the range. Because contextual fragments are not subject to the normal content model restrictions of the DOM, it is possible to make a contextual fragment for HTML like <li>HI</li>.

Internet Explorer's TextRange object is not sufficiently flexible to surround arbitrary nodes that do not immediately contain text (such as a <tbody> node). As a result, when the W3C range API is not available, a much more complex solution is required.

Metamorph also includes workarounds for a number of bugs in Internet Explorer's handling of innerHTML, and its DOM implementation. For full information, the Internet Explorer workarounds are well-documented in the code.


Because is not always possible to insert a Metamorph directly into the DOM, the main initial API is outerHTML.


If you like, you can disable the range API by using an environment variable:

MetamorphENV = { DISABLE_RANGE_API: true }

The current implementation of the range API in many browsers is slower than the alternative implementation inside Metamorph.js. It is a good idea to benchmark your application and decide whether you'd like to disable the range API.


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