# LiveAssign
[](https://hex.pm/packages/live_assign)
[](https://hexdocs.pm/live_assign/)
[](https://github.com/schrockwell/live_assign/blob/master/LICENSE)
LiveAssign improves state management by sprinkling functionality on top of Phoenix LiveView.
It doesn't _replace_ the LiveView way of doing things, but instead _augments_ it with conventions. LiveAssign can be added to any view or component without affecting existing functionality, and its features can be opted-in as they are needed.
Combine it with [LiveEvent](https://hexdocs.pm/live_event/) for an altogether improved component-building experience.
LiveViews and LiveComponents both gain:
- **State** assigns which are defined in the module
- **Reactive functions** that are automatically invoked upon state changes
- **Runtime checks** with developer-friendly error messages
LiveComponents also gain additional functionality:
- **Props** which are assigns that are strictly passed in to the component
- **Slot** props to represent component slots
- **Event** props that integrate with [LiveEvent](https://hexdocs.pm/live_event/)
Here are a couple examples showing off these features. For complete details, please reference [the docs](https://hexdocs.pm/live_assign/).
## LiveComponent Example
```elixir
defmodule MyAppWeb.UserProfileComponent do
use Phoenix.LiveComponent
use LiveAssign.LiveComponent
prop :profile
prop :show_avatar?, default: false
state :age
state :expand_details?, default: false
slot :inner_block
def handle_event("toggle-details", _, socket) do
{:noreply, put_state(socket, expand_details?: not socket.assigns.expand_details?)}
end
@react to: :profile
defp put_age(socket) do
age = trunc(Date.diff(Date.utc_today(), socket.assigns.profile.birthday) / 365)
put_state(socket, age: age)
end
# ...
end
```
The `:profile` assign is a **required prop**. If it is not passed in, a helpful runtime error will occur.
The `:id` assign is also a required prop, but it is implicitly defined by `use LiveAssign.LiveComponent`, because every LiveComponent requires an `:id`.
The `:show_avatar?` assign is an **optional prop** that defaults to `false` when unspecified.
The `:expand_details?` and `:age` assigns are **state**. They can be modified via `put_state/2`.
The `:inner_block` assign is a **slot prop**. It is required but can be made optional with the `required?: false` option.
The `put_age/1` function is a **reactive callback**. It is automatically evaluated whenever the value of the `:profiles` state changes. The function can react to prop changes and state changes.
## LiveView Example
```elixir
defmodule MyAppWeb.ProfileIndexLive do
use Phoenix.LiveView
use LiveAssign.LiveView
state :profiles, default: load_profiles()
state :profile_count
@react to: :profiles
defp put_profile_count(socket) do
put_state(socket, profile_count: length(socket.assigns.profiles))
end
defp load_profiles, do: # ...
# ...
end
```
The `:profiles` and `:profile_count` assigns are **state**. They can be modified throughout the LiveView lifecycle, and reactive functions can respond to their changes.
The `put_profile_count/1` callback is a **reactive function** that is automatically invoked as soon as any changes occur to the `:profiles` state.
## Installation
The package can be installed by adding `live_assign` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:live_assign, "~> 0.3.0"}
]
end
```
