JS's LocalStorage in Elixir - A super simple intro to GenServer for js devs

local_storage.ex

defmodule LocalStorage do
  use GenServer

  # API

  def start_link do
    GenServer.start_link(__MODULE__, %{}, name: __MODULE__)
  end

  def set_item(key, val) do
    GenServer.cast(__MODULE__, {:set_item, key, val})
  end

  def get_item(key) do
    GenServer.call(__MODULE__, {:get_item, key})
  end

  def remove_item(key) do
    GenServer.cast(__MODULE__, {:remove_item, key})
  end

  def clear() do
    GenServer.cast(__MODULE__, :clear)
  end

  def all() do
    GenServer.call(__MODULE__, :all)
  end

  # GenServer Callbacks

  def handle_cast({:set_item, key, val}, store) do
    {:noreply, Map.put(store, key, val)}
  end

  def handle_cast({:remove_item, key}, store) do
    {:noreply, Map.drop(store, key)}
  end

  def handle_cast(:clear, state) do
    {:noreply, %{}}
  end

  def handle_call({:get_item, key}, _from, store) do
    {:reply, Map.get(store, key), store}
  end
  
  def handle_call(:all, _from, state) do
    {:reply, state, state}
  end
end

Usage:

iex

iex(1)> c "local_storage.ex"
[LocalStorage]
iex(2)> LocalStorage.start_link
{:ok, #PID<0.102.0>}
iex(3)> LocalStorage.all
%{}
iex(4)> LocalStorage.set_item(:foo, "bar")
:ok
iex(5)> LocalStorage.get_item(:foo)
"bar"
iex(6)> LocalStorage.get_item(:nope)
nil
iex(7)> LocalStorage.all
%{foo: "bar"}
iex(8)> LocalStorage.clear
:ok
iex(9)> LocalStorage.all
%{}

what happens when your server crashes? :)