Pardon me if this has been asked but I searched and didn't find the specific implementation of my problem.

Anyway, I'm currently learning high-order functions in JavaScript and I'm at the array.prototype.filter function. I understand its purpose (as its name so conveniently implies) but I'm having trouble implementing this:

So, say I have an array of names, like this:

var names = [Anna, Bob, Charles, Daniel,

         Allison, Beatrice, Cindy, Fiona];

And then I want to, say, filter that array by all entries that start with the letter A. I'm aware of the fact that I could do this:

var filteredNames = names.filter(function(word) {

    return word[0] === A;

});

And that would work just fine. But say I want to be less explicit and make it more adaptable to more situations. Say I want to program the filtering so that I can say return only the entries that have the letter x at index [y], for example return only the entries that have the letter F at index[3].

How can I achieve that?