I'm currently working on a site with a contact tab on the top of the site, and am trying to create text to expand/collapse above the tab. The js code I am trying to use is from web standards and near the bottom of that link. I have added all the required ID's and CSS as stated in the comments. The JS code however is returning an error "NOT_FOUND_ERR: DOM Exception 8" at the line of remove child in this part of the code
Code:
stmjr_collapse.prototype.swapAnchorText = function(newText) {
//      Swap out title text on the anchor
        this.anchor.title = newText;
//      Clear out all children of the anchor
        var len = this.anchor.childNodes.length;
        for (i = 0; i < len; i++) {
            this.anchor.removeChild(this.anchor.childNodes[i])
        }
//      Add the new link text to the anchor
        this.anchor.appendChild(document.createTextNode(newText));
}
How can I fix this error and get the code working properly?

Thank you in advance!