LiveView Code Review

Quick Reference

Issue Type	Reference
mount, handle_params, handle_event, handle_async	references/lifecycle.md
When to use assigns vs streams, AsyncResult	references/assigns-streams.md
Function vs LiveComponent, slots, attrs	references/components.md
Authorization per event, phx-value trust	references/security.md

Review Checklist

Critical Issues

• No socket copying into async functions (extract values first)
• Every handle_event validates authorization
• No sensitive data in assigns (visible in DOM)
• phx-value data is validated (user-modifiable)

Lifecycle

• Subscriptions wrapped in connected?(socket)
• handle_params used for URL-based state
• handle_async handles :loading and :error states

Data Management

• Streams used for large collections (100+ items)
• temporary_assigns for data not needed after render
• AsyncResult patterns for loading states

Components

• Function components preferred over LiveComponents
• LiveComponents preserve :inner_block in update/2
• Slots use proper attr declarations
• phx-debounce on text inputs

Valid Patterns (Do NOT Flag)

• Empty mount returning {:ok, socket} - Valid for simple LiveViews
• Using assigns for small lists - Streams only needed for 100+ items
• LiveComponent without update/2 - Default update/2 assigns all
• phx-click without phx-value - Event may not need data
• Inline function in heex - Valid for simple transforms

Context-Sensitive Rules

Issue	Flag ONLY IF
Missing debounce	Input is text/textarea AND triggers server event
Use streams	Collection has 100+ items OR is paginated
Missing auth check	Event modifies data AND no auth in mount

Critical Anti-Patterns

Socket Copying (MOST IMPORTANT)

# BAD - socket copied into async function
def handle_event("load", _, socket) do
  Task.async(fn ->
    user = socket.assigns.user  # Socket copied!
    fetch_data(user.id)
  end)
  {:noreply, socket}
end

# GOOD - extract values first
def handle_event("load", _, socket) do
  user_id = socket.assigns.user.id
  Task.async(fn ->
    fetch_data(user_id)  # Only primitive copied
  end)
  {:noreply, socket}
end

Missing Authorization

# BAD - trusts phx-value without auth
def handle_event("delete", %{"id" => id}, socket) do
  Posts.delete_post!(id)  # Anyone can delete any post!
  {:noreply, socket}
end

# GOOD - verify authorization
def handle_event("delete", %{"id" => id}, socket) do
  post = Posts.get_post!(id)

  if post.user_id == socket.assigns.current_user.id do
    Posts.delete_post!(post)
    {:noreply, stream_delete(socket, :posts, post)}
  else
    {:noreply, put_flash(socket, :error, "Unauthorized")}
  end
end

Before Submitting Findings

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