Skip to content

Blogging On Rails

Everything on Rails!

Stimulus + Trix: Convert Emoji Short Codes To Unicode Characters On The Fly

Let’s Add an Emoji Converter to Trix with Stimulus

We’ve been exploring using Stimulus to add interactivity to our apps. Let’s use Stimulus to watch for typing changes, and convert an emoji short code into the actual glyph, such as :smiley: to 😀

Getting Started

I’ve uploaded my code to Github, so you can follow along with an actual Rails project if you’re ever stuck, or comment below.

Let’s create a new rails app (using rails 5.2.0.rc2):

rails new trix_emoji --webpack=stimulus

We’re going to add a controller called Documents and a show method on it. We need to add the appropriate routes in routes.rb.

Rails.application.routes.draw do
  resource :document

And the controller, documents_controller.rb:

class DocumentsController < ApplicationController 
  def show

And we’ll add a view, documents/show.html.erb:

<h1>Trix Emoji Converter 2000</h1> 

Configuring Trix With Yarn and Webpack

Let’s add Trix to our package.json file with Yarn:

$ yarn add trix

Then, we’ll add Trix to our webpack root file, javascripts/packs/applications.js:

import "trix/dist/trix.css";
import { Trix } from "trix"

The first line imports the CSS for the trix-editor element, and the next line imports the Javascript code that makes the editor run.

You’ll want to make sure to add the webpacker stylesheet and javascript tags to layouts/application.html.erb:

<%= javascript_pack_tag 'application', 'data-turbolinks-track': 'reload' %>
<%= stylesheet_pack_tag 'application', 'data-turbolinks-track': 'reload' %>

And now we can add our Trix Editor to our html:


Adding Stimulus

Let’s add the proper annotations to our HTML for our Trix controller:

<trix-editor data-controller="emoji-converter" 

The editor will be a target for the controller so that we can filter out events that might not correspond the current controller instance. Here is the skeleton code for the emoji_converter_controller.js:

import { Controller } from "stimulus"

export default class extends Controller {
  static targets = ["editor"]

  connect() {
    window.addEventListener("trix-change", this.trixChange.bind(this))

  trixChange(event) {
    if ( == this.editorTarget) {

When the controller connects to the dom, it starts listening for the trix-change event, which is fired after a change occurs in a trix editor. We make sure that the change is from our controller’s editor, and then we’ll scan through the text to look for the emoji short codes.

Let’s Find those Short Codes :smiley:

Inside the trixChange function, we’ll go through every character of the editor’s text, and we’ll see if we find a short code. If we find a one, we’ll see if we have the short code to emoji mapping. If we have a mapping, we’ll replace the text, and stop scanning, because replacing the text is going to create another change event, which will allow us to look again very shortly.

Let’s add a small set of supported emojis to our controller, by creating a dictionary in our connect method:

connect() {
    window.addEventListener("trix-change", this.trixChange.bind(this))
    this.supportedEmojis = {
      ":smiley:" : "😀",
      ":stuck_out_tongue_winking_eye:" : "😜",
      ":bowtie:" : "🤵",

Then in the change method, we’ll process each change and look for a short code.

trixChange(event) {
    if ( == this.editorTarget) {

We’re going to get the text of the document from our editor:

      let stringDoc = this.editorTarget.editor.getDocument().toString()

We’ll set up some variables to keep track of what we’ve found as we go over the string:

      var foundItem = false
      var foundStart = -1
      var foundText = ""

      // Iterating over every 16 bit unicode character, 
      // since `for (var letter of stringDoc)` method won't work
      // in this particular situation.
      for (var count = 0; count<stringDoc.length; count++) {

We’ll look at every letter, and check to see if it’s a colon (:) character:

        let letter = stringDoc[count];
        if (letter == ":") {
          if (foundItem) {
            foundText += letter

If we found a supported emoji, we’ll replace the short code. Otherwise, we’ll ignore it, and keep looking. We also keep track of a new colon character, and any text we find between colons.

            let emoji = this.supportedEmojis[foundText]
            if (emoji) {
              this.editorTarget.editor.setSelectedRange([foundStart, count + 1])
              return // break out and wait for next trix-change event
            } else {
              foundItem = false
              foundStart = -1
              foundText = ""
          } else {
            foundItem = true
            foundStart = count
            foundText = letter
        } else if (foundItem) {
          // If we come across a space, it's not a supported emoji, so reset
          if (letter == " ") {
            foundItem = false
            foundStart = -1
            foundText = ""
          } else {
            foundText += letter

And now Trix will convert short codes into Emoji!

This is a fun and simple example, but I imagine it could be used for more complicated interactivity, like looking for @username values, or automatically linking to anther project.

Again, You can find all the code on Github here:

Feel free to leave comments or questions below.

Want To Learn More?

Try out some more of my Stimulus.js Tutorials.

[convertkit form=818581]

Leave a Reply

Copyright © 2022 John Beatty. All rights reserved.