Aufgeräumter

Array.prototype.unique = function() {
    var uniqueKeys  = {},
        uniqueArray = [],
        items = this.length

    while( items ) 
        uniqueKeys[this[--items]] = true

    for( var key in uniqueKeys ) 
        if (uniqueKeys.hasOwnProperty(key)) uniqueArray.push(key)

    return uniqueArray
}