Phoenix.LiveView - Phoenix LiveView

Overview

A LiveView is a process that receives events, updates its state, and renders updates to a page as diffs. LiveView begins as a regular HTTP request and HTML response, and then upgrades to a stateful view on client connect, guaranteeing a regular HTML page even if JavaScript is disabled. Socket assigns are stateful values kept on the server side.

Life-cycle

The LiveView life-cycle follows this sequence:

mount/3 - Invoked on both initial HTTP render and WebSocket connection
handle_params/3 - Invoked after mount and on live patch events
render/1 - Renders the template whenever state changes

Callbacks

mount/3

@callback mount(
  params :: unsigned_params() | :not_mounted_at_router,
  session :: map,
  socket :: Socket.t()
) :: {:ok, Socket.t()} | {:ok, Socket.t(), keyword()}

The LiveView entry-point called twice: once for initial page load and again to establish the live socket.

params

map | :not_mounted_at_router

A map of string keys containing query params and router path parameters. Returns :not_mounted_at_router if not mounted at router.

session

map

The connection session containing private data set by the application.

socket

Socket.t()

The LiveView socket.

return

{:ok, socket} | {:ok, socket, options}

Returns updated socket with optional configuration:

:temporary_assigns - Assigns reset after each render
:layout - Optional layout override

Example:

def mount(_params, _session, socket) do
  if connected?(socket), do: :timer.send_interval(1000, self(), :tick)
  {:ok, assign(socket, date: :calendar.local_time())}
end

render/1

@callback render(assigns :: Socket.assigns()) :: Phoenix.LiveView.Rendered.t()

Renders a template. Invoked whenever LiveView detects new content must be rendered and sent to the client.

assigns

map

The socket assigns map.

return

Phoenix.LiveView.Rendered.t()

Must return a template defined via the ~H sigil.

Example:

def render(assigns) do
  ~H"""
  <div>Hello {@name}!</div>
  """
end

handle_params/3

@callback handle_params(
  unsigned_params(),
  uri :: String.t(),
  socket :: Socket.t()
) :: {:noreply, Socket.t()}

Invoked after mount and whenever there is a live patch event.

params

map

Current parameters including router params and query params.

uri

string

The current URI from the client.

socket

Socket.t()

The LiveView socket.

handle_event/3

@callback handle_event(
  event :: binary,
  unsigned_params(),
  socket :: Socket.t()
) :: {:noreply, Socket.t()} | {:reply, map, Socket.t()}

Invoked to handle events sent by the client.

event

string

The event name (e.g., “save”, “delete”).

params

map

The event payload as a map.

socket

Socket.t()

The LiveView socket.

return

{:noreply, socket} | {:reply, map, socket}

Returns updated socket, optionally with a reply map sent back to client.

handle_info/2

@callback handle_info(msg :: term, socket :: Socket.t()) :: {:noreply, Socket.t()}

Invoked to handle messages from other Elixir processes.

msg

term

The message received from another process.

socket

Socket.t()

The LiveView socket.

handle_async/3

@callback handle_async(
  name :: term,
  async_fun_result :: {:ok, term} | {:exit, term},
  socket :: Socket.t()
) :: {:noreply, Socket.t()}

Invoked when the result of a start_async/3 operation is available.

name

term

The name given to start_async/3.

result

{:ok, result} | {:exit, reason}

The async function result wrapped in :ok or :exit.

socket

Socket.t()

The LiveView socket.

handle_call/3

@callback handle_call(msg :: term, {pid, reference}, socket :: Socket.t()) ::
  {:noreply, Socket.t()} | {:reply, term, Socket.t()}

Invoked to handle synchronous call messages from other Elixir processes via GenServer.call/2.

msg

term

The message sent via GenServer.call/2.

from

{pid, reference}

The caller’s PID and reply reference.

socket

Socket.t()

The LiveView socket.

return

{:noreply, socket} | {:reply, term, socket}

Either :noreply for no response or :reply with a return value for the caller.

Example:

def handle_call(:get_state, _from, socket) do
  {:reply, socket.assigns, socket}
end

handle_cast/2

@callback handle_cast(msg :: term, socket :: Socket.t()) ::
  {:noreply, Socket.t()}

Invoked to handle asynchronous cast messages from other Elixir processes via GenServer.cast/2.

msg

term

The message sent via GenServer.cast/2.

socket

Socket.t()

The LiveView socket.

return

{:noreply, socket}

Returns updated socket.

Example:

def handle_cast({:update_data, data}, socket) do
  {:noreply, assign(socket, :data, data)}
end

terminate/2

@callback terminate(reason, socket :: Socket.t()) :: term
  when reason: :normal | :shutdown | {:shutdown, :left | :closed | term}

Invoked when the LiveView is terminating. Use this to clean up resources.

reason

:normal | :shutdown | {:shutdown, reason}

The termination reason:

:normal - Normal termination
:shutdown - Application shutdown
{:shutdown, :left} - User navigated away
{:shutdown, :closed} - Connection closed

socket

Socket.t()

The LiveView socket.

return

term

Return value is ignored.

Example:

def terminate(_reason, socket) do
  # Clean up resources
  :ok
end

Functions

assign/3

Adds a key-value pair to socket assigns.

assign(socket, :name, "Elixir")

socket

Socket.t()

The LiveView socket.

key

atom

The assign key.

value

any

The assign value.

return

Socket.t()

Updated socket with new assign.

assign_new/3

Assigns a key with value from function if one does not yet exist.

assign_new(socket, :current_user, fn -> Accounts.get_user!(user_id) end)

socket

Socket.t()

The LiveView socket.

key

atom

The assign key.

fun

function

Function returning the value (0 or 1 arity).

update/3

Updates an existing key with a function.

update(socket, :count, &(&1 + 1))

socket

Socket.t()

The LiveView socket.

key

atom

The assign key to update.

fun

function

Function receiving current value and returning updated value.

push_event/3

Pushes an event to the client.

push_event(socket, "scores", %{points: 100, user: "josé"})

socket

Socket.t()

The LiveView socket.

event

string

The event name.

payload

map

The event data.

opts

keyword

default:"[]"

Options:

:dispatch - :before or :after patch (default: :after)

push_navigate/2

Annotates the socket for navigation to another LiveView in the same live_session.

push_navigate(socket, to: "/")
push_navigate(socket, to: "/", replace: true)

socket

Socket.t()

The LiveView socket.

opts

keyword

Options:

:to (required) - The path to navigate to
:replace - Replace browser history (default: false)

push_patch/2

Annotates the socket for navigation within the current LiveView.

push_patch(socket, to: "/")
push_patch(socket, to: "/", replace: true)

socket

Socket.t()

The LiveView socket.

opts

keyword

Options:

:to (required) - The path to patch to
:replace - Replace browser history (default: false)

redirect/2

Annotates the socket for redirect to a destination path.

redirect(socket, to: "/")
redirect(socket, external: "https://example.com")

socket

Socket.t()

The LiveView socket.

opts

keyword

Options:

:to - Local path to redirect to
:external - External URL to redirect to
:status - HTTP status code (default: 302)

put_flash/3

Adds a flash message to the socket.

put_flash(socket, :info, "It worked!")
put_flash(socket, :error, "You can't access that page")

socket

Socket.t()

The LiveView socket.

kind

atom

The flash type (:info, :error, etc.).

msg

string

The flash message.

stream/4

Assigns a new stream or inserts items into an existing stream.

stream(socket, :songs, songs)
stream(socket, :songs, songs, at: 0, limit: 10)

socket

Socket.t()

The LiveView socket.

name

atom | string

The stream name.

items

Enumerable.t()

Items to insert.

opts

keyword

default:"[]"

Options:

:at - Index to insert items (default: -1)
:reset - Reset stream on client (default: false)
:limit - Limit items in UI

stream_insert/4

Inserts a new item or updates an existing item in the stream.

stream_insert(socket, :songs, song)
stream_insert(socket, :songs, song, at: 0, limit: -10)

socket

Socket.t()

The LiveView socket.

name

atom | string

The stream name.

item

any

Item to insert or update.

opts

keyword

default:"[]"

Options:

:at - Index to insert item (default: -1)
:limit - Limit items in UI

stream_delete/3

Deletes an item from the stream.

stream_delete(socket, :songs, song)

socket

Socket.t()

The LiveView socket.

name

atom | string

The stream name.

item

any

Item to delete.

stream_delete_by_dom_id/3

Deletes a stream item by its DOM ID.

stream_delete_by_dom_id(socket, :songs, "songs-123")

socket

Socket.t()

The LiveView socket.

name

atom | string

The stream name.

string

The DOM ID of the item to delete.

stream_configure/3

Configures a stream with options.

stream_configure(socket, :songs, dom_id: &("song-#{&1.id}"))

socket

Socket.t()

The LiveView socket.

name

atom | string

The stream name.

opts

keyword

Options:

:dom_id - Function to generate DOM IDs

assign_async/3

Assigns keys asynchronously using a task.

assign_async(socket, :org, fn -> {:ok, %{org: fetch_org!(slug)}} end)

socket

Socket.t()

The LiveView socket.

keys

atom | list

Key or list of keys to assign.

func

function

Function returning {:ok, assigns} or {:error, reason}.

opts

keyword

default:"[]"

Options:

:supervisor - Task.Supervisor to use
:reset - Remove previous results (default: false)

start_async/3

Wraps a function in an asynchronous task.

start_async(socket, :my_task, fn -> fetch_data() end)

socket

Socket.t()

The LiveView socket.

name

term

Name for the async operation.

func

function

Function to execute asynchronously.

opts

keyword

default:"[]"

Options:

:supervisor - Task.Supervisor to use

send_update/3

Asynchronously updates a LiveComponent with new assigns.

send_update(Cart, id: "cart", status: "cancelled")
send_update(pid, Cart, id: "cart", status: "cancelled")

pid

default:"self()"

The LiveView process ID.

module

atom

The LiveComponent module.

assigns

keyword | map

Assigns to update (must include :id).

cancel_async/3

Cancels one or more async operations.

cancel_async(socket, :org)
cancel_async(socket, [:org, :profile])
cancel_async(socket, async_result, :cancel)

socket

Socket.t()

The LiveView socket.

keys

atom | list | AsyncResult.t()

Async key(s) to cancel or an AsyncResult struct.

reason

term

default:"{:shutdown, :cancel}"

The cancellation reason.

attach_hook/4

Attaches a function by name for a lifecycle stage.

attach_hook(socket, :my_hook, :handle_event, fn event, params, socket ->
  # Handle event
  {:cont, socket}
end)

socket

Socket.t()

The LiveView socket.

name

atom

Hook name.

stage

atom

Lifecycle stage: :handle_params, :handle_event, :handle_info, :handle_async, :after_render.

fun

function

Hook function.

connected?/1

Returns true if the socket is connected.

if connected?(socket), do: subscribe_to_updates()

socket

Socket.t()

The LiveView socket.

return

boolean

true if connected via WebSocket, false during initial HTTP render.

get_connect_params/1

Accesses the connect params sent by the client.

get_connect_params(socket)["time_zone"]

socket

Socket.t()

The LiveView socket.

return

map | nil

Connect params on connected mount, nil when disconnected.

get_connect_info/2

Gets connection metadata by key.

get_connect_info(socket, :peer_data)
get_connect_info(socket, :x_headers)

socket

Socket.t()

The LiveView socket.

key

atom

Connection info key (:peer_data, :x_headers, :uri, :user_agent, etc.).

return

term | nil

Connection metadata value or nil.

static_changed?/1

Checks if static assets have changed since the LiveView was rendered.

if static_changed?(socket) do
  push_navigate(socket, to: "/")
end

socket

Socket.t()

The LiveView socket.

return

boolean

true if static assets changed during the connection.

clear_flash/1

Clears all flash messages.

clear_flash(socket)

socket

Socket.t()

The LiveView socket.

clear_flash/2

Clears a specific flash message key.

clear_flash(socket, :info)

socket

Socket.t()

The LiveView socket.

key

atom

Flash key to clear.

detach_hook/3

Detaches a hook by ID and lifecycle stage.

detach_hook(socket, :my_hook, :handle_event)

socket

Socket.t()

The LiveView socket.

atom

Hook identifier.

stage

atom

Lifecycle stage (:mount, :handle_params, :handle_event, :handle_info, :after_render).

allow_upload/3

Allows an upload for the provided name.

allow_upload(socket, :avatar, accept: ~w(.jpg .jpeg), max_entries: 2)
allow_upload(socket, :avatar, accept: :any)

socket

Socket.t()

The LiveView socket.

name

atom

Upload name.

opts

keyword

Options:

:accept (required) - File extensions list or :any
:max_entries - Maximum files (default: 1)
:max_file_size - Maximum bytes (default: 8MB)
:chunk_size - Chunk size in bytes (default: 64KB)
:auto_upload - Auto-upload on selection (default: false)
:external - Function for external uploads
:progress - Progress callback function

Core Modules

Routing & Controllers

Testing

Configuration

Uploads

​Overview

​Life-cycle

​Callbacks

​mount/3

​render/1

​handle_params/3

​handle_event/3

​handle_info/2

​handle_async/3

​handle_call/3

​handle_cast/2

​terminate/2

​Functions

​assign/3

​assign_new/3

​update/3

​push_event/3

​push_navigate/2

​push_patch/2

​redirect/2

​put_flash/3

​stream/4

​stream_insert/4

​stream_delete/3

​stream_delete_by_dom_id/3

​stream_configure/3

​assign_async/3

​start_async/3

​send_update/3

​cancel_async/3

​attach_hook/4

​connected?/1

​get_connect_params/1

​get_connect_info/2

​static_changed?/1

​clear_flash/1

​clear_flash/2

​detach_hook/3

​allow_upload/3

Build docs developers (and LLMs) love

Overview

Life-cycle

Callbacks

mount/3

render/1

handle_params/3

handle_event/3

handle_info/2

handle_async/3

handle_call/3

handle_cast/2

terminate/2

Functions

assign/3

assign_new/3

update/3

push_event/3

push_navigate/2

push_patch/2

redirect/2

put_flash/3

stream/4

stream_insert/4

stream_delete/3

stream_delete_by_dom_id/3

stream_configure/3

assign_async/3

start_async/3

send_update/3

cancel_async/3

attach_hook/4

connected?/1

get_connect_params/1

get_connect_info/2

static_changed?/1

clear_flash/1

clear_flash/2

detach_hook/3

allow_upload/3