Simple hiccup implementation in JavaScript

hiccup-examples.js

// First argument (or array element for nested arrays) is tag name.
// Second can optionally be an object, in which case it is used to 
// supply attributes. All others are added to the tag's body.
html("p", {"class": "foo"}, "hello world", "!")
'<p class="foo">hello world!</p>'

// Shortcuts for denoting id and class attributes
html("p#foo.bar.baz", "hello world!")
'<p id="foo" class="bar baz">hello world!</p>'

// Arrays are used for nested tags
html("p", ["span.highlight", "Important!"], " less important")
'<p><span class="highlight">Important!</span> less important</p>'

// Simple list example
html("ol", ["li", "first"], ["li", "second"])
'<ol><li>first</li><li>second</li></ol>'

// List example with array comprehension - requires JS 1.7
// (but will also combine nicely with Array.map and friends)
html("ul", [["li", item] for each (item in [1, 2, 3])])
'<ul><li>1</li><li>2</li><li>3</li></ul>'

// Pass multiple arrays as arguments to get an element list 
// instead of a single element
html(["p", "first paragraph"], ["p", "second paragraph"])
'<p>first paragraph</p><p>second paragraph</p>'

hiccup.js

exports.html = function() {
    var buffer = [];
    build(arguments, buffer);
    return buffer.join("");
}

function build(list, buffer) {
    var index = 0;
    var length = list.length;
    if (typeof list[index] === "string") {
        var tag = splitTag(list[index++]);
        var attr = tag[1];
        tag = tag[0];
        if (isObject(list[index])) {
            mergeAttributes(attr, list[index++]);
        }
        buffer.push("<", tag);
        for (var key in attr) {
            buffer.push(" ", key, "=\"", attr[key], "\"");
        }
        buffer.push(">");
        buildRest(list, index, buffer);
        buffer.push("</", tag, ">");
    } else {
        buildRest(list, index, buffer);
    }
}

function buildRest(list, index, buffer) {
    var length = list.length;
    while (index < length) {
        var item = list[index++];
        if (isArray(item)) {
            build(item, buffer);
        } else {
            buffer.push(item);
        }
    }
}

function isObject(item) {
    return item instanceof Object && item.constructor !== Array;
}

function isArray(item) {
    return item instanceof Object && item.constructor === Array;
}

function mergeAttributes(attr1, attr2) {
    for (var key in attr2) {
        if (!attr1.hasOwnProperty(key)) {
            attr1[key] = attr2[key];
        } else if (key === "class") {
            attr1[key] += " " + attr2[key];
        }
    }
}

function splitTag(tag) {
    var attr = {};
    var match = tag.match(/([^\s\.#]+)(?:#([^\s\.#]+))?(?:\.([^\s#]+))?/);
    if (match[2]) attr.id = match[2];
    if (match[3]) attr["class"] = match[3].replace(/\./g, " ");
    return [match[1], attr];
}