# Inertia.js Phoenix Adapter [](https://hex.pm/packages/inertia) [](https://hexdocs.pm/inertia/readme.html)
The Elixir/Phoenix adapter for [Inertia.js](https://inertiajs.com/).
## Table of Contents
- [Installation](#installation)
- [Rendering responses](#rendering-responses)
- [Setting up the client-side](#setting-up-the-client-side)
- [Lazy data evaluation](#lazy-data-evaluation)
- [Shared data](#shared-data)
- [Validations](#validations)
- [Flash messages](#flash-messages)
- [CSRF protection](#csrf-protection)
- [Server-side rendering](#server-side-rendering-experimental)
## Installation
The package can be installed by adding `inertia` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:inertia, "~> 0.10.0"}
]
end
```
Add your desired configuration in your `config.exs` file:
```elixir
# config/config.exs
config :inertia,
# The Phoenix Endpoint module for your application. This is used for building
# asset URLs to compute a unique version hash to track when something has
# changed (and a reload is required on the frontend).
endpoint: MyAppWeb.Endpoint,
# An optional list of static file paths to track for changes. You'll generally
# want to include any JavaScript assets that may require a page refresh when
# modified.
static_paths: ["/assets/app.js"],
# The default version string to use (if you decide not to track any static
# assets using the `static_paths` config). Defaults to "1".
default_version: "1",
# Enable server-side rendering for page responses (requires some additional setup,
# see instructions below). Defaults to `false`.
ssr: false,
# Whether to raise an exception when server-side rendering fails (only applies
# when SSR is enabled). Defaults to `true`.
#
# Recommended: enable in non-production environments and disable in production,
# so that SSR failures will not cause 500 errors (but instead will fallback to
# CSR).
raise_on_ssr_failure: config_env() != :prod
```
This library includes a few modules to help render Inertia responses:
- [`Inertia.Plug`](https://hexdocs.pm/inertia/Inertia.Plug.html): a plug for detecting Inertia.js requests and preparing the connection accordingly.
- [`Inertia.Controller`](https://hexdocs.pm/inertia/Inertia.Controller.html): controller functions for rendering Inertia.js-compatible responses.
- [`Inertia.HTML`](https://hexdocs.pm/inertia/Inertia.HTML.html): HTML components for Inertia-powered views.
To get started, import `Inertia.Controller` in your controller helper and `Inertia.HTML` in your html helper:
```diff
# lib/my_app_web.ex
defmodule MyAppWeb do
def controller do
quote do
use Phoenix.Controller, namespace: MyAppWeb
+ import Inertia.Controller
end
end
def html do
quote do
use Phoenix.Component
+ import Inertia.HTML
end
end
end
```
Then, install the plug in your browser pipeline:
```diff
# lib/my_app_web/router.ex
defmodule MyAppWeb.Router do
use MyAppWeb, :router
pipeline :browser do
plug :accepts, ["html"]
+ plug Inertia.Plug
end
end
```
Next, replace the title tag in your layout with the `<.inertia_title>` component, so that the client-side library will keep the title in sync, and add the `<.inertia_head>` component:
```diff
# lib/my_app_web/components/layouts/root.html.heex
<!DOCTYPE html>
<html lang="en" class="[scrollbar-gutter:stable]">
<head>
- <.live_title><%= assigns[:page_title] %></.live_title>
+ <.inertia_title><%= assigns[:page_title] %></.inertia_title>
+ <.inertia_head content={@inertia_head} />
</head>
```
You're now ready to start rendering inertia responses!
## Rendering responses
Rendering an Inertia.js response looks like this:
```elixir
defmodule MyAppWeb.ProfileController do
use MyAppWeb, :controller
def index(conn, _params) do
conn
|> assign_prop(:text, "Hello world")
|> render_inertia("ProfilePage")
end
end
```
The `assign_prop` function allows you defined props that should be passed in to the component. The `render_inertia` function accepts the conn, the name of the component to render, and an optional map containing more initial props to pass to the page component.
This action will render an HTML page containing a `<div>` element with the name of the component and the initial props, following Inertia.js conventions. On subsequent requests dispatched by the Inertia.js client library, this action will return a JSON response with the data necessary for rendering the page.
## Setting up the client-side
The [Inertia.js docs](https://inertiajs.com/client-side-setup) provide a good general walk-through on how to setup your JavaScript assets to boot your Inertia app. If you're new to Inertia, we recommend checking that out to familiarize yourself with how it all works. Here we'll provide some guidance on getting your Phoenix app with esbuild configured for basic client-side rendering (and further down, we'll delve into server-side rendering).
To get started, install the Inertia.js library for the frontend framework of your choice. In these instructions we'll use React, but the process is similiar for other Inertia-compatible frameworks, like Vue or Svelte.
```
cd assets
npm install @inertiajs/react react react-dom
```
Replace the contents of your `app.js` file with the Inertia boot function and rename it to `app.jsx` (since we are using JSX).
```javascript
// assets/js/app.jsx
import React from "react";
import axios from "axios";
import { createInertiaApp } from "@inertiajs/react";
import { createRoot } from "react-dom/client";
axios.defaults.xsrfHeaderName = "x-csrf-token";
createInertiaApp({
resolve: async (name) => {
return await import(`./pages/${name}.jsx`);
},
setup({ App, el, props }) {
createRoot(el).render(<App {...props} />);
},
});
```
The example above assumes your pages live in the `assets/js/pages` directory and have a default export with page component, like this:
```javascript
// assets/js/pages/Dashboard.jsx
import React from "react";
const Dashboard = () => {
return (
<div>
{/* ... page contents ...*/}
</div>
);
}
export default Dashboard;
```
Next, make some adjustments to your esbuild config:
- Ensure the version is >= 0.19.0 (this is required for glob-style imports for your pages)
- Update your entrypoint filename to the correct `.jsx` extension
- Ensure your build `--target` is at least `es2020`
```elixir
# config/config.exs
config :esbuild,
version: "0.21.5",
my_app: [
args: ~w(js/app.jsx --bundle --target=es2020 --outdir=../priv/static/assets --external:/fonts/* --external:/images/*),
cd: Path.expand("../assets", __DIR__),
env: %{"NODE_PATH" => Path.expand("../deps", __DIR__)}
]
```
If you updated your esbuild version, you'll need to run `mix esbuild.install` to fetch the new version.
## Lazy data evaluation
If you have expensive data for your props that may not always be required (that is, if you plan to use [partial reloads](https://inertiajs.com/partial-reloads)), you can wrap your expensive computation in a function and pass the function reference when setting your Inertia props. You may use either an anonymous function (or named function reference) and optionally wrap it with the `Inertia.Controller.inertia_lazy/1` function.
> [!NOTE]
> `inertia_lazy` props will _only_ be included the when explicitly requested in a partial
> reload. If you want to include the prop on first visit, you'll want to use a
> bare anonymous function or named function reference instead. See below for
> examples of how prop assignment behaves.
Here are some specific examples of how the methods of lazy data evaluation differ:
```elixir
conn
# ALWAYS included on first visit...
# OPTIONALLY included on partial reloads...
# ALWAYS evaluated...
|> assign_prop(:cheap_thing, cheap_thing())
# ALWAYS included on first visit...
# OPTIONALLY included on partial reloads...
# ONLY evaluated when needed...
|> assign_prop(:expensive_thing, fn -> calculate_thing() end)
|> assign_prop(:another_expensive_thing, &calculate_another_thing/0)
# NEVER included on first visit...
# OPTIONALLY included on partial reloads...
# ONLY evaluated when needed...
|> assign_prop(:super_expensive_thing, inertia_lazy(fn -> calculate_thing() end))
```
## Shared data
To share data on every request, you can use the `assign_prop/2` function inside of a shared plug in your response pipeline. For example, suppose you have a `UserAuth` plug responsible for fetching the currently-logged in user and you want to be sure all your Inertia components receive that user data. Your plug might look something like this:
```elixir
defmodule MyApp.UserAuth do
import Inertia.Controller
import Phoenix.Controller
import Plug.Conn
def authenticate_user(conn, _opts) do
user = get_user_from_session(conn)
# Here we are storing the user in the conn assigns (so
# we can use it for things like checking permissions later on),
# AND we are assigning a serialized represention of the user
# to our Inertia props.
conn
|> assign(:user, user)
|> assign_prop(:user, serialize_user(user))
end
# ...
end
```
Anywhere this plug is used, the serialized `user` prop will be passed to the Inertia component.
## Validations
Validation errors follow some specific conventions to make wiring up with Inertia's form helpers seamless. The `errors` prop is managed by this library and is always included in the props object for Inertia components. (When there are no errors, the `errors` prop will be an empty object).
The `assign_errors` function is how you tell Inertia what errors should be represented on the front-end. You can either pass an `Ecto.Changeset` struct or a bare map to the `assign_errors` function.
```elixir
def update(conn, params) do
case MyApp.Settings.update(params) do
{:ok, _settings} ->
conn
|> put_flash(:info, "Settings updated")
|> redirect(to: ~p"/settings")
{:error, changeset} ->
conn
|> assign_errors(changeset)
|> redirect(to: ~p"/settings")
end
end
```
The `assign_errors` function will automatically convert the changeset errors into a shape compatible with the client-side adapter. Since Inertia.js expects a flat map of key-value pairs, the error serializer will flatten nested errors down to compound keys:
```javascript
{
"name" => "can't be blank",
// Nested errors keys are flattened with a dot seperator (`.`)
"team.name" => "must be at least 3 characters long",
// Nested arrays are zero-based and indexed using bracket notation (`[0]`)
"items[1].price" => "must be greater than 0"
}
```
Errors are automatically preserved across redirects, so you can safely respond with a redirect back to page where the form lives to display form errors.
If you need to construct your own map of errors (rather than pass in a changeset), be sure it's a flat mapping of atom (or string) keys to string values like this:
```elixir
conn
|> assign_errors(%{
name: "Name can't be blank",
password: "Password must be at least 5 characters"
})
```
## Flash messages
This library automatically includes Phoenix flash data in Inertia props, under the `flash` key.
For example, given the following controller action:
```elixir
def update(conn, params) do
case MyApp.Settings.update(params) do
{:ok, _settings} ->
conn
|> put_flash(:info, "Settings updated")
|> redirect(to: ~p"/settings")
{:error, changeset} ->
conn
|> assign_errors(changeset)
|> redirect(to: ~p"/settings")
end
end
```
When Inertia (or the browser) redirects to the `/settings` page, the Inertia component will receive the flash props:
```javascript
{
"component": "...",
"props": {
"flash": {
"info": "Settings updated"
},
// ...
}
}
```
## CSRF protection
This library automatically sets the `XSRF-TOKEN` cookie for use by the Axios client on the front-end. Since Phoenix expects to receive the CSRF token via the `x-csrf-token` header, you'll need to configure Axios in your front-end JavaScript to use that header name:
```javascript
// assets/js/app.js
import axios from "axios";
axios.defaults.xsrfHeaderName = "x-csrf-token";
// the rest of your Inertia client code...
```
## Server-side rendering (Experimental)
The Inertia.js client library comes with with server-side rendering (SSR) support, which means you can have your Inertia-powered client hydrate HTML that has been pre-rendered on the server (instead of performing the initial DOM rendering).
> [!NOTE]
> The steps for enabling SSR in Phoenix are similar to other backend frameworks, but instead of running a separate Node.js server process to render HTML, this library spins up a pool of Node.js process workers to handle SSR calls. We'll highlight those differences below.
### Add a server-side rendering module
To get started, you'll need to create a JavaScript module that exports a `render` function to perform the actual server-side rendering of pages. For the purpose of these instructions, we'll assume you're using React. The steps would be similar for other front-end environments supported by Inertia.js, such as [Vue](https://github.com/CallumVass/inertia_vue) and [Svelte](https://github.com/tonydangblog/phoenix-inertia-svelte).
Suppose your main `app.jsx` file looks something like this:
```js
// assets/js/app.jsx
import React from "react";
import { createInertiaApp } from "@inertiajs/react";
import { createRoot } from "react-dom/client";
createInertiaApp({
resolve: async (name) => {
return await import(`./pages/${name}.jsx`);
},
setup({ App, el, props }) {
createRoot(el).render(<App {...props} />);
},
});
```
You'll need to create a second JavaScript file (alongside your `app.jsx`) that exports a `render` function. Let's name it `ssr.jsx`.
```js
// assets/js/ssr.jsx
import React from "react";
import ReactDOMServer from "react-dom/server";
import { createInertiaApp } from "@inertiajs/react";
export function render(page) {
return createInertiaApp({
page,
render: ReactDOMServer.renderToString,
resolve: async (name) => {
return await import(`./pages/${name}.jsx`);
},
setup: ({ App, props }) => <App {...props} />,
});
}
```
This is similar to the server entry-point [documented here](https://inertiajs.com/server-side-rendering#add-server-entry-point), except we are simply exporting a render function instead of starting a Node.js server process.
Next, configure esbuild to compile the `ssr.jsx` bundle.
```diff
# config/config.exs
config :esbuild,
version: "0.21.5",
app: [
args: ~w(js/app.jsx --bundle --target=es2020 --outdir=../priv/static/assets --external:/fonts/* --external:/images/*),
cd: Path.expand("../assets", __DIR__),
env: %{"NODE_PATH" => Path.expand("../deps", __DIR__)}
],
+ ssr: [
+ args: ~w(js/ssr.jsx --bundle --platform=node --outdir=../priv --format=cjs),
+ cd: Path.expand("../assets", __DIR__),
+ env: %{"NODE_PATH" => Path.expand("../deps", __DIR__)}
+ ]
```
Add the `ssr` build to the watchers in your dev environment, alongside the other asset watchers:
```diff
# config/dev.exs
config :my_app, MyAppWeb.Endpoint,
# Binding to loopback ipv4 address prevents access from other machines.
# Change to `ip: {0, 0, 0, 0}` to allow access from other machines.
http: [ip: {127, 0, 0, 1}, port: 4000],
check_origin: false,
code_reloader: true,
debug_errors: true,
secret_key_base: "4Z2yyTu6Uy8AM+MguG3oldEf4aIdswR2BsCm1OtqDK0lEv++T02KktRaXfMbC/Zs",
watchers: [
esbuild: {Esbuild, :install_and_run, [:app, ~w(--sourcemap=inline --watch)]},
+ ssr: {Esbuild, :install_and_run, [:ssr, ~w(--sourcemap=inline --watch)]},
tailwind: {Tailwind, :install_and_run, [:my_app, ~w(--watch)]}
]
```
Add the `ssr` build step to the asset build and deploy scripts.
```diff
# mix.exs
defp aliases do
[
setup: ["deps.get", "ecto.setup", "assets.setup", "assets.build"],
"ecto.setup": ["ecto.create", "ecto.migrate", "run priv/repo/seeds.exs"],
"ecto.reset": ["ecto.drop", "ecto.setup"],
test: ["ecto.create --quiet", "ecto.migrate --quiet", "test"],
"assets.setup": ["tailwind.install --if-missing", "esbuild.install --if-missing"],
- "assets.build": ["tailwind app", "esbuild app"],
+ "assets.build": ["tailwind app", "esbuild app", "esbuild ssr"],
"assets.deploy": [
"tailwind app --minify",
"esbuild app --minify",
+ "esbuild ssr",
"phx.digest"
]
]
end
```
As configured, this will place the generated `ssr.js` bundle into the `priv` directory. Since it's generated code, add it to your `.gitignore` file.
```diff
# .gitignore
+ /priv/ssr.js
```
### Configuring your app for server-rendering
Now that you have a Node.js module capable of server-rendering your pages, let's tell the Inertia.js Phoenix library to use SSR.
First, you'll need to add the `Inertia.SSR` module to your application supervision tree.
```diff
# lib/my_app/application.ex
defmodule MyApp.Application do
use Application
@impl true
def start(_type, _args) do
children = [
MyAppWeb.Telemetry,
MyApp.Repo,
{DNSCluster, query: Application.get_env(:MyApp, :dns_cluster_query) || :ignore},
{Phoenix.PubSub, name: MyApp.PubSub},
# Start the Finch HTTP client for sending emails
{Finch, name: MyApp.Finch},
# Start a worker by calling: MyApp.Worker.start_link(arg)
# {MyApp.Worker, arg},
+ # Start the SSR process pool
+ # You must specify a `path` option to locate the directory where the `ssr.js` file lives.
+ {Inertia.SSR, path: Path.join([Application.app_dir(:my_app), "priv"])},
# Start to serve requests, typically the last entry
MyAppWeb.Endpoint,
]
```
Then, update your Inertia Elixir configuration to enable SSR.
```diff
# config/config.exs
config :inertia,
# The Phoenix Endpoint module for your application. This is used for building
# asset URLs to compute a unique version hash to track when something has
# changed (and a reload is required on the frontend).
endpoint: MyAppWeb.Endpoint,
# An optional list of static file paths to track for changes. You'll generally
# want to include any JavaScript assets that may require a page refresh when
# modified.
static_paths: ["/assets/app.js"],
# The default version string to use (if you decide not to track any static
# assets using the `static_paths` config). Defaults to "1".
default_version: "1",
# Enable server-side rendering for page responses (requires some additional setup,
# see instructions below). Defaults to `false`.
- ssr: false
+ ssr: true
# Whether to raise an exception when server-side rendering fails (only applies
# when SSR is enabled). Defaults to `true`.
#
# Recommended: enable in non-production environments and disable in production,
# so that SSR failures will not cause 500 errors (but instead will fallback to
# CSR).
raise_on_ssr_failure: config_env() != :prod
```
In production, be sure to set `NODE_ENV` environment variable to `production`, so that the SSR script is cached for optimal performance.
### Client side hydration
[Follow the instructions from the Inertia.js docs](https://inertiajs.com/server-side-rendering#client-side-hydration) for updating your client-side code to hydrate the pre-rendered HTML coming from the server.
Using our example React script from above, the adaptation looks like this:
```diff
// assets/js/app.jsx
import React from "react";
import { createInertiaApp } from "@inertiajs/react";
- import { createRoot } from "react-dom/client";
+ import { hydrateRoot } from "react-dom/client";
createInertiaApp({
resolve: async (name) => {
return await import(`./pages/${name}.jsx`);
},
setup({ App, el, props }) {
- createRoot(el).render(<App {...props} />);
+ hydrateRoot(el, <App {...props} />);
},
});
```
---
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