Study of 3 ways to implement the same function, with different programming styles

getElementByTagName.js

/**
 * Similar to root.getElementsByTagName(tagName), but:
 *
 *    1. Returns root if root.tagName == tagName.
 *    2. Returns only one element (the first if there are many).
 *    3. Can take an array of tagName if there are alternatives.
 *
 * @param {Element}                 root            Root node from which we start the search
 * @param {string|Array.<string>}   tagNameOrArray  Tag name we're looking for
 */

function getElementByTagNameImperative(root, tagNameOrArray) {

    if (YAHOO.lang.isArray(tagNameOrArray)) {
        for (var tagNameIndex = 0; tagNameIndex < tagNameOrArray.length; tagNameIndex++) {
            var tagName = tagNameOrArray[tagNameIndex];
            var result = ORBEON.util.Dom.getElementByTagName(root, tagName);
            if (result != null) return result;
        }
        return null;
    } else {
        if (root.tagName.toLowerCase() == tagNameOrArray) {
            return root;
        } else {
            var matches = root.getElementsByTagName(tagNameOrArray);
            return matches.length != 0 ? matches[0] : null;
        }
    }
}

function getElementByTagNameFunctional(root, tagNameOrArray) {

    return _(tagNameOrArray).chain()
        .match(
            _.isArray, function(tagNameArray) {
                return _(tagNameArray).chain()
                    .map(_.bind(ORBEON.util.Dom.getElementByTagName, null, root))
                    .compact()
                    .first()
                    .value()
            },
            function(tagName) {
                return _(tagName).match(
                    root.tagName.toLowerCase(), root,
                    function() {
                        return _(tagName).chain()
                            .take(root.getElementsByTagName, root)
                            .first()
                            .value();
                    }
                );
            })
        .match(_.isUndefined, null)
        .value();
}

function getElementByTagNamePragmatic(root, tagNameOrArray) {

    var result = _.isArray(tagNameOrArray)
        ? _(tagNameOrArray).chain()
            .map(_.bind(arguments.callee, null, root))
            .compact()
            .first()
            .value()
        : root.tagName.toLowerCase() == tagNameOrArray
            ? root
            : root.getElementsByTagName(tagNameOrArray)[0];
    return _.isUndefined(result) ? null : result;
}