JavaScript: lightweight selector implementation

gistfile1.txt

//
// Returns first element that matches CSS selector {expr}.
// Querying can optionally be restricted to {container}’s descendants
//

function $( expr, container ) {
    return typeof expr === 'string' ? ( container || document ).querySelector( expr ) : expr || null;
}

//
// Returns all elements that match CSS selector {expr} as an array.
// Querying can optionally be restricted to {container}’s descendants
//

function $$( expr, container ) {
    return [].slice.call( ( container || document ).querySelectorAll( expr ) );
}