Andrew Timberlake Andrew Timberlake

Hi, I’m Andrew, a programer and entrepreneur from South Africa, founder of Sitesure for monitoring websites, APIs, and background jobs.
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Add a tooltip component to Phoenix

This post will show you how to add a custom tooltip component to your Phoenix project that uses the PopperJS library.

You can view all the code in a simple project on Github. See a diff from the initial install at 922ecca..30e278a

This post wil also demonstrate how to incorporate any Javascript library that requires bindings to an element. In Phoenix that is done through Hooks.

The Component

In the CoreComponents module, we have a tooltip component. I have defined a class attribute to allow style overrides, but with a defaults of nil so it’s not required
I have also defined a slot which will take the content of the tooltip. The HTML of the tooltip is just a div element. This element has the phx-hook attribute which tells Phoenix which set of hooks to bind this element with (more under Javascript).
Every element that is bound with hooks requires an id. Because we need to use tooltips easily, I have added a random ID generated through a random_id/1 function. The function takes a prefix just to help avoid collisions, even though we’re using random bytes. The end result looks like this <div id="tt_F3P5wcGhyQA"…

defmodule PhoenixTooltipsWeb.CoreComponents do
  # ...
  attr :class, :string, default: nil
  slot :inner_block, required: true

  def tooltip(assigns) do
    <div id={random_id("tt")} class={["tooltip", @class]} role="tooltip" phx-hook="TooltipHook">
      <%= render_slot(@inner_block) %>
      <div class="arrow" data-popper-arrow></div>

  def random_id(prefix) do
    prefix <> "_" <> (:crypto.strong_rand_bytes(8) |> Base.url_encode64(padding: false))
  # ...

The Live View

Every demonstration needs a contrived example. Here I am producing a grid of HTML colours using the HTML standard colour names. The block is a colour and the tooltip is the name of the colour.

defmodule PhoenixTooltipsWeb.PageLive do
  use PhoenixTooltipsWeb, :live_view

  def mount(_params, _session, socket) do
    {:ok, assign(socket, :color_names, color_names())}

  def color_names() do

The Heex template iterates through all the colour names and adds a button (so you can see the tooltip on focus/blur) with the colour as the background and a tooltip with the colour name as it’s text.

<div class="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-4">
  <%= for color <- @color_names do %>
    <button class="h-16 rounded-none" style={"background-color:#{color}"}>
      <.tooltip class="px-4 py-2 font-medium text-white bg-black border border-white rounded-md">
        <%= color %>
  <% end %>


The CSS is almost directly from the PopperJS tutorial.
The .tooltip class (included in the component by default) is initially set to display:none and then, when given the data-show attribute, is set to display:block. The rest is the styling of the arrow and it’s position.

.tooltip {
  display: none;

.tooltip[data-show] {
  display: block;

.tooltip > .arrow,
.tooltip > .arrow:before {
  position: absolute;
  width: 8px;
  height: 8px;
  background: inherit;
  border: inherit;
  border-bottom: none;
  border-right: none;

.tooltip > .arrow {
  visibility: hidden;

.tooltip > .arrow::before {
  visibility: visible;
  content: '';
  transform: rotate(45deg);

.tooltip[data-popper-placement^='top'] > .arrow {
  bottom: -5.5px;

.tooltip[data-popper-placement^='bottom'] > .arrow {
  top: -5.5px;

.tooltip[data-popper-placement^='left'] > .arrow {
  right: -5.5px;

.tooltip[data-popper-placement^='right'] > .arrow {
  left: -5.5px;

The Javascript

The first step is to install the PopperJS library via npm. the --prefix assets is needed to place the node related files in the assets/ directory.

$ npm install @popperjs/core --prefix assets

I have created a Tooltip javascript class to manage the lifescycle of the tooltip. This can be pasted into the top of your app.js file or in it’s own file and imported into app.js

The constructor sets up the tooltip by creating a popperInstance, linking the tooltip element to it’s parent, and setting event listeners on the parent to show/hide the tooltip. For this example we are using mouseenter and focus to show the tooltip and mouseleave and blur to hide it. The class also stores destructors so that event lsiteners are removed when the tooltip is removed from the DOM (preventing possible memory leaks).

import { createPopper } from '@popperjs/core';

// A class to manage the tooltip lifecycle.
class Tooltip {
  showEvents = ['mouseenter', 'focus'];
  hideEvents = ['mouseleave', 'blur'];

  constructor($tooltip) {
    this.$tooltip = $tooltip;
    this.$parent = $tooltip.parentElement;
    this.popperInstance = createPopper(this.$parent, $tooltip, {
      modifiers: [
          name: 'offset',
          options: {
            offset: [0, -8],
    this.destructors = [];

    // For each show event, add an event listener on the parent element
    //   and store a destructor to call removeEventListener
    //   when the tooltip is destroyed.
    this.showEvents.forEach((event) => {
      const callback =;
      this.$parent.addEventListener(event, callback);
      this.destructors.push(() =>
        this.$parent.removeEventListener(event, callback)

    // For each hide event, add an event listener on the parent element
    //   and store a destructor to call removeEventListener
    //   when the tooltip is destroyed.
    this.hideEvents.forEach((event) => {
      const callback = this.hide.bind(this);
      this.$parent.addEventListener(event, callback);
      this.destructors.push(() =>
        this.$parent.removeEventListener(event, callback)

  // The show method adds the data-show attribute to the tooltip element,
  //   which makes it visible (see CSS).
  show() {
    this.$tooltip.setAttribute('data-show', '');

  // Update the popper instance so the tooltip position is recalculated.
  update() {

  // The hide method removes the data-show attribute from the tooltip element,
  //   which makes it invisible (see CSS).
  hide() {

  // The destroy method removes all event listeners
  //   and destroys the popper instance.
  destroy() {
    this.destructors.forEach((destructor) => destructor());

Phoenix Hooks are where the magic happens.

Our TooltipHook listens for three of the six possible lifecycle hooks.

Important: You need to update the let liveSocket = … line in app.js and add , hooks: Hooks which is not there by default.

// ...
const Hooks = {
  TooltipHook: {
    mounted() {
      this.el.tooltip = new Tooltip(this.el);
    updated() {
    destroyed() {

// ...
let liveSocket = new LiveSocket('/live', Socket, {
  params: { _csrf_token: csrfToken },
  // add the Hooks object
  hooks: Hooks,
// ...

By using Phoenix Client hooks we are able to connect the element of a component to a Javascript client library, add event listeners, and provide custom interaction.

See all the code on Github.

12 Sep 2023

How to use SASS/SCSS with Webpack in Phoenix 1.4

Phoenix 1.4 is on it’s way and one of the big changes is that webpack is replacing brunch. If you are a SASS fan then this is how to update the default Webpack configuration to use SASS (SCSS flavour).

Install NPM packages

The first step is to install the node-sass and sass-loader packages from NPM.

Using Yarn

$ yarn add node-sass sass-loader --dev

Using NPM

$ npm install node-sass sass-loader --save-dev

Update webpack.config.js

Update the assets/webpack.config.js file with a change to chain the sass-loader plugin after the css-loader.

diff --git a/assets/webpack.config.js b/assets/webpack.config.js
index 5225785..4c14948 100644
--- a/assets/webpack.config.js
+++ b/assets/webpack.config.js
@@ -26,8 +26,18 @@ module.exports = (env, options) => ({
-      test: /\.css$/,
-      use: [MiniCssExtractPlugin.loader, 'css-loader']
+      test: /\.scss$/,
+      use: [
+        MiniCssExtractPlugin.loader,
+        {
+          loader: 'css-loader',
+          options: {}
+        },
+        {
+          loader: 'sass-loader',
+          options: {}
+        }
+      ]

Update app.css

Rename your assets/css/app.css to assets/css/app.scss.

$ mv assets/css/app.css assets/css/app.scss

Update app.js

Because the CSS files are loaded by Webpack through the javascript file, you need to update the css import path as well.

diff --git a/assets/js/app.js b/assets/js/app.js
index 8ee7177..0aa55a0 100644
--- a/assets/js/app.js
+++ b/assets/js/app.js
@@ -1,7 +1,7 @@
 // We need to import the CSS so that webpack will load it.
 // The MiniCssExtractPlugin is used to separate it out into
 // its own CSS file.
-import css from "../css/app.css"
+import css from "../css/app.scss"

 // webpack automatically bundles all modules in your
 // entry points. Those entry points can be configured

Build assets

Finally test your assets build.

$ node node_modules/webpack/bin/webpack.js --mode development
17 Jun 2018

Use Phoenix 1.4 Now

With Phoenix 1.4 announced at ElixirConf EU ( I was keen to try it out. I was specifically interested in seeing the new Webpack integration. Getting started with Phoenix 1.4 is really quite easy.

Uninstall the existing Phoenix 1.3 archive

From the README,

Remove any previously installed phx_new archives so that Mix will pick up the local source code. This can be done with mix archive.uninstall phx_new or by simply deleting the file, which is usually in ~/.mix/archives/.

Clone the Phoenix master repo

$ git clone

Build and install the Phoenix archive

$ cd phoenix/installer
$ MIX_ENV=prod mix do, archive.install

Generate your new Phoenix 1.4 app

Run mix my_app

Your mix.exs deps will now look like this:

defp deps do
    {:phoenix, github: "phoenixframework/phoenix", override: true},

When Phoenix 1.4 is released, you can just update this line to:

defp deps do
    {:phoenix, "~> 1.4.0"},

Revert back to the Phoenix 1.3 installer

Reverting to the 1.3 installer is as easy as uninstalling and reinstalling the Phoenix archive.


mix archive.uninstall phx_new-1.3.0
mix archive.install
16 Jun 2018