Fastest, most lightweight, pseudo-random generator (for HTML IDs)?

# produces something like "-576460752302382141"
iex> :timer.tc fn -> Enum.each(1..1000, fn _ -> System.unique_integer() |> Integer.to_string end) end
{746, :ok}

# produces something like "FE404" <- I like this one
# note: grows larger and larger the longer VM operates, but won't exceed `(NoSchedulers + 1) × (2⁶⁴ - 1)`
iex> :timer.tc fn -> Enum.each(1..1000, fn _ -> System.unique_integer([:positive]) |> Integer.to_string(16) end) end
{787, :ok}

# produces something like "4D37AE7D3E6865A26A64"
iex> :timer.tc fn -> Enum.each(1..1000, fn _ -> :rand.bytes(10) |> Base.encode16() end) end
{1358, :ok}

# produces something like "cd2acfc8-90f2-4c19-9440-5207f49102f2"
iex> :timer.tc fn -> Enum.each(1..1000, fn _ -> Ecto.UUID.generate() end) end
{1722, :ok}

And then there is also Enum.with_index/2 that can be used to give unique ids for a collection of elements.

And I think the latest trend is to actually use fewer ids and instead use aria or data attributes. Summary: You may not need HTML ID's

Why would it be excessive? All that System.unique_integer/0,1 promises is that it will not return the same value twice for the same options, so it’s actually a very cheap function, it essentially just bumps a thread-local counter and returns it.

Liveview does require idd for a few things, for example when you use hooks.

If you use System.unique_integer() how do you know what the ID is? And if you don’t know what the ID is how is it being used, like why is it there?

Exactly. I use meaningful strings for IDs and collect all IDs strings into one module as macros to avoid name collision.

The requirement comes from LV. It tracks dom node livecycles via ids (so that a new id means a new livecycle) e.g. for hooks as well as for streams. Sometimes being unique is enough of a property to make those things work, even if there’s no further targeting of those ids. It’s enough that they happen to be different.

When using a JS hook.

this.el.id

Don’t LV ids need to be deterministic? I’ve been warned not to use any kind of non-deterministic generation of ids on here before.

Enum.with_index is a good solution. There is also %Form{}.index. Otherwise if there is a schema involved I just schema_name_#{@schema.id}.

I’d still recommend it be something the caller sets and is meaningful. IE

attr(:id, :string, required: true)
...
<div id={"my-component-#{@id}"}

I will have:

defmodule MyAppWeb.Ids do
  defmacro my_component(id) do
    quote do
      "my-component-#{unquote(id)}"
    end
  end
end

and use Ids.my_component(@id) everywhere in the liveview. With another level of indirection, I can avoid potential name collision.