Stop mounting your LiveView twice
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Phoenix LiveView mounts twice on first page load — once for the static HTTP dead render and again when the WebSocket connects. The common fix of guarding data loads with `connected?/1` avoids double queries but breaks SEO, link previews, and no-JS fallback by leaving the dead render empty. This post explains why the double mount exists, what `connected?/1` actually costs, and introduces an experimental fork that parks the dead-render socket in a short-lived GenServer and redeems it on WebSocket connect — skipping the second mount entirely. The fork adds an `on_connect/1` callback for connection-only side effects (subscriptions, timers, presence) and provides migration patterns for data loads, connect params, and real-time data. The upstream Phoenix team is working on a more complete 'adoptable LiveViews' solution (issue #3551), but this fork serves as an interim stopgap.
