How can I get a list of all categories in GetEventStore?

Question

From streams like these:

• sales-sale102
• sales-sale103
• sales-sale104
• users-8989
• users-8990

Get somethig like this:

[ "sales", "users"]

Answer 1

Thanks to nissbran from GitHub

fromStream('$streams')
.when({
$init: function () {
    return []
},
$any: function (s, e) {
    var category = e.streamId.split("-")[0];

    if (s.includes(category))
        return;

    s.push(category);
}
})