thornify.js

// JavaScript functions to replace "th" by the letter thorn throughout
// a document.  Use this with `thornifyDoc(window.document)`.

// Written by David A. Madore, 2022-04-02.  Public Domain.

function thornifyString(s) {
    return s.replace(/T[Hh]/g, "\u00DE").replace(/th/g, "\u00FE");
}

function thornifyDoc(doc) {
    var body = doc.body;
    var walker = doc.createTreeWalker(body, NodeFilter.SHOW_ELEMENT | NodeFilter.SHOW_TEXT, null, false);
    var node = walker.nextNode();
    while ( node ) {
	if ( node.nodeType == Node.TEXT_NODE ) {
	    var thisnode = node;
	    node = walker.nextNode();
	    var str = thornifyString(thisnode.nodeValue);
	    thisnode.parentNode.replaceChild(doc.createTextNode(str), thisnode);
	} else if ( node.nodeType == Node.ELEMENT_NODE
		    && ( node.localName == "pre"
			 || node.localName == "code"
			 || node.localName == "script"
			 || node.localName == "style" ) ) {
	    do {
		node = walker.nextSibling();
		if ( node )
		    break;
		node = walker.parentNode();
		if ( ! node )
		    break;
	    } while ( true );
	} else
	    node = walker.nextNode();
    }
}