Simple selector

function $(selector, context) {
    context = context || document;

    var firstChar  = selector[0],
        nameOnly   = selector.substring(1, selector.length),
        maybeId    = firstChar === "#",
        maybeClass = firstChar === ".",
        isSimple   = /^[\w-]*$/.test(nameOnly),
        qsaRe      = /^(.+[\#\.\s\[\*>:,]|[\[:])/,
        element    =
            maybeId    && isSimple ?
                context.getElementById(nameOnly)         :
            maybeClass && isSimple ?
                context.getElementsByClassName(nameOnly) :
            qsaRe.test(selector) ?
                context.querySelectorAll(selector)       :
                context.getElementsByTagName(selector)
    ;

    return element;
}