Answer by Dennis Allen for How do I check if an array includes a value in JavaScript?

Just another option

// usage: if ( ['a','b','c','d'].contains('b') ) { ... }
Array.prototype.contains = function(value){
    for (var key in this)
        if (this[key] === value) return true;
    return false;
}

Be careful because overloading javascript array objects with custom methods can disrupt the behavior of other javascripts, causing unexpected behavior.