process external text using iframe

Standard browser scripts are very restricted as to their input: they mostly operate on the HTML in the current web page, and have no native means of accessing other data. HTML itself however has a couple of mechanisms for loading external documents, which can be used as proxies for a script.

This loads text from an external file into an invisible iframe object, then with JavaScript gets the text from the object, processes it, and displays it in a different part of the web page. HTML could also be similarly obtained as text or traversed as an object tree.

the result:

complications

document load sequence

At the time the main document is loaded, any child iframe referring to an external document is empty. This is because if the external document takes time to download, the rest of the document should be rendered first.

The onload attribute of the iframe can be set to execute a function when the document arrives. So the trick is to set a timer to wait until this event fires, then to get and render the iframe contents.