How to update element inside List with ImmutableJS?

The most appropriate case is to use both findIndex and update methods.

list = list.update(
  list.findIndex(function(item) { 
    return item.get("name") === "third"; 
  }), function(item) {
    return item.set("count", 4);
  }
); 

P.S. It’s not always possible to use Maps. E.g. if names are not unique and I want to update all items with the same names.