Phoenix Liveview using LocalStorage or SessionStorage

Sometimes we want to fetch or store data in localStorage or sessionStorage, we can fetch/store this data using LiveView hooks. These hooks allow for interoperability with JavaScript and grant us the ability to interact with a liveview during its lifecycle.

For storing the data, we will call a JavaScript hook inside a liveview function to store the value of a counter.

For fetching the data, we will be using the reconnected hook to fetch data from localStorage or sessionStorage. In this post we will be using sessionStorage as the data is wiped when we close the tab. If you wanted to persist the data, localStorage is what you are looking for. Both storages use the same function getItem(key) where we provide a key which hopefully has the values we are looking for.

For more information regarding sessionStorage and localStorage see the Mozilla Docs

Cloning the Demo Project

Let’s clone the demo Phoenix LiveView app. The main branch will only contain the minimal amount of setup without implementing any hooks:

git clone

For the complete solution check out the complete branch.

Setting up the Hooks

NOTE: All hooks need to be defined above the following line let liveSocket = new LiveSocket("/live", Socket, {params: {_csrf_token: csrfToken}})

Initializing our empty hooks object to be populated later:

let hooks = {}

We need to add our hooks to the liveSocket:

let liveSocket = new LiveSocket("/live", Socket, {
  params: {_csrf_token: csrfToken},
  hooks: hooks,

Saving State on Button Click

To save the state of our counter on button click we need to write a custom hook.

In app.js, we are going to create a hook called saveCount:

hooks.saveCount = {
  mounted() {
    this.handleEvent("saveCount", ({ count }) =>
      sessionStorage.setItem("count", count)

saveCount uses the mounted hook so it gets attached as the component is mounted.

For the handle_event function we use a new function called push_event which will invoke the JavaScript hook we called saveCount

def handle_event("inc", _session, socket) do
  count = socket.assigns.count + 1
  socket = socket |> assign(count: count)
  {:noreply, push_event(socket, "saveCount", %{count: count})}

To wire up our button we need to add a unique ID as well as the hook:

<button id="inc-button" phx-click="inc" phx-hook="saveCount">Increment</button>

We should now see the value of count being incremented in sessionStorage as well as on the page

Restoring state on Reconnection

To restore the state from sessionStorage we need to create a new hook that I will call restore:

hooks.restore = {
  mounted() {
    count = sessionStorage.getItem("count")
    this.pushEvent("restore", {count: count})

This hook will call our restore event in the liveview which looks like:

def handle_event("restore", %{"count" => count}, socket) do
  count = String.to_integer(count)
  socket = socket |> assign(count: count)
  {:noreply, socket}

NOTE: Values in sessionStorage are strings and we need to properly convert to the correct type

We do need to handle cases where we have no value in the sessionStorage, we can do that by explcitly handling nil values above the original handle_event call:

def handle_event("restore", %{"count" => nil}, socket), do: {:noreply, socket}

def handle_event("restore", %{"count" => count}, socket) do
  count = String.to_integer(count)
  socket = socket |> assign(count: count)
  {:noreply, socket}

In order to actually call the restore hook we need to add a unique ID to the element and attach our hook to it:

<section class="phx-hero" id="page-live" phx-hook="restore" >

We now have a way to restore data from sessionStorage or localStorage into our LiveView!

To test this out, we can go into the developer settings and manually add key-value pair to sessionStorage

example: count: 100

When we refresh the page, the counter should reflect the value in the sessionStorage


This is how to store and restore data in a LiveView using Hooks and sessionStorage. If you found it helpful, reach out on twitter or share with your friends!

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