Maria D. Campbell

Importing Images in React 2.0: Jest (and Babel 7)

Note December 3, 2018: There were some changes I had to make after adding support for image imports into React because it caused “side effects”. Please visit my article entitled The Jest Side Effect and The New Babel Config to get the whole picture. There were some issues along the way due to breaking changes in Babel 7 which affected Jest, React, and ESLint. Unless you are using create-react-app, your workflow might have to be adjusted depending on what support you want to provide in any given application. I have brought all resources together in the repository for the second edition of my custom React Workflow on Github. Please visit issues to learn more.

Yesterday I added an image to a new project. I tried to implement it using the “image” workflow I had set up based on the first edition of my custom React Workflow (without create-react-app), and it DID NOT WORK!

Of course not. I am not using the same dependency versions I did more than a year ago. Things always change, but now they are changing more quickly than ever! Not only are they changing, but it seems that whatever is released needs to be tweaked as well.

It’s not necessarily that something isn’t good when it is released, but it still has to be able to play well with its “playmates”. That doesn’t always end up being the case. Old playmates disappear, and new ones come in to replace them.

For instance, I used to be able to create an images folder in the root of my projects and an index.js file in the root of the images folder, then export the images from index.js so that I could use them anywhere in my project. That’s because way back when, images had to be in the same folder as all other files needed for production. That (usually) was a folder called src. But because I used a lot of images, and liked to have an organized folder structure in my dist (build) folder, I created my own image workflow to make that happen.

Now that there is Babel 7 and the Babel configuration has drastically changed, certain modern JavaScript syntax in our code is no longer recognized when we are developing inside our text editors or IDEs. This means that TDD software such as Jest is affected as well.

I just completed the second edition of my custom React Workflow the other day. It works well for what it offers out of the box. However, just as with the first edition, I only included a favicon and no images. I ended up taking images into consideration for the workflow later.

I would like to discuss the changes in the custom workflow (providing support for images) that have taken place since I wrote the article Importing images in React on October 7, 2017. A few things (like the folder structure) may be the same, but I can no longer export my images from an index.js file in the images folder. I think it might have something to do with what my Babel 7 configuration is no longer providing me, but I have to investigate further to find out the answers.

If you are going to or already started to use React 16.6+(I currently use React 16.6.3 in my workflow), Webpack 4+ (I use 4.3.0), Babel 7, Jest (I use 23.6.0), and ESLint (I use 5.9.0), and want to ADD IMAGES to your projects, please follow the steps I discuss here for starters, and ignore the Jest configuration in both the first and second edition of my custom workflow. If you only are adding a favicon or no image at all, then keep the configuration provided in the second edition.

In the presentation/documentation for the second edition of my custom workflow for React, I have the following dependencies and devDependencies in my package.json:

  name: "speech-to-text-app",
  version: "0.0.1",
  private: true,
  description: ""A voice controlled notes app that allows you to take notes by recording your voice"",
  main: "index.js",
  scripts: {
    test: "jest",
    lint: "eslint .",
    clean: "rimraf dist",
    cleanSrc: "rimraf dist/src",
    start: "webpack-dev-server --mode development --config config/webpack.base.config.js --open --hot --history-api-fallback --env.PLATFORM=local --env.VERSION=stag",
    predeploy: "webpack --mode production --config config/ --env.PLATFORM=production --env.VERSION=stag --progress",
    deploy: "gh-pages -d dist"
  jest: {
    setupFiles: [
    moduleNameMapper: {
      \.(pdf|jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$: "<rootDir>/__mocks__/fileMock.js",
      \.(css|less|scss)$: "identity-obj-proxy"
  author: "Maria D. Campbell",
  license: "ISC",
  dependencies: {
    @fortawesome/fontawesome-svg-core: "^1.2.8",
    @fortawesome/free-brands-svg-icons: "^5.5.0",
    @fortawesome/free-regular-svg-icons: "^5.5.0",
    @fortawesome/free-solid-svg-icons: "^5.5.0",
    @fortawesome/react-fontawesome: "^0.1.3",
    core-js: "^2.5.7",
    gh-pages: "^2.0.1",
    react: "^16.6.3",
    react-dom: "^16.6.3",
    react-loadable: "^5.5.0"
  devDependencies: {
    @babel/core: "^7.1.6",
    @babel/plugin-proposal-class-properties: "^7.1.0",
    @babel/plugin-proposal-export-namespace-from: "^7.0.0",
    @babel/plugin-proposal-throw-expressions: "^7.0.0",
    @babel/plugin-syntax-dynamic-import: "^7.0.0",
    @babel/polyfill: "^7.0.0",
    @babel/preset-env: "^7.1.5",
    @babel/preset-react: "^7.0.0",
    @babel/register: "^7.0.0",
    autoprefixer: "^9.3.1",
    babel-core: "^7.0.0-bridge.0",
    babel-eslint: "^10.0.1",
    babel-jest: "^23.6.0",
    babel-loader: "^8.0.4",
    clean-webpack-plugin: "^1.0.0",
    copy-webpack-plugin: "^4.6.0",
    css-loader: "^1.0.1",
    enzyme: "^3.7.0",
    eslint: "^5.9.0",
    eslint-config-airbnb: "^17.1.0",
    eslint-loader: "^2.1.1",
    eslint-plugin-import: "^2.14.0",
    eslint-plugin-jsx-a11y: "^6.1.2",
    eslint-plugin-react: "^7.11.1",
    file-loader: "^2.0.0",
    html-webpack-plugin: "^3.2.0",
    identity-obj-proxy: "^3.0.0",
    jest: "^23.6.0",
    jest-enzyme: "^7.0.1",
    mini-css-extract-plugin: "^0.4.4",
    node-sass: "^4.10.0",
    optimize-css-assets-webpack-plugin: "^5.0.1",
    postcss: "^7.0.5",
    postcss-loader: "^3.0.0",
    prop-types: "^15.6.2",
    raf: "^3.4.1",
    react-test-renderer: "^16.6.1",
    regenerator-runtime: "^0.12.1",
    rimraf: "^2.6.2",
    sass-loader: "^7.1.0",
    style-loader: "^0.23.1",
    uglifyjs-webpack-plugin: "^2.0.1",
    url-loader: "^1.1.2",
    webpack: "^4.3.0",
    webpack-cli: "^3.1.2",
    webpack-dev-server: "^3.1.10",
    webpack-manifest-plugin: "^2.0.4",
    webpack-merge: "^4.1.4",
    webpack-visualizer-plugin: "^0.1.11",
    workbox-webpack-plugin: "^3.6.3"

My workflow provides support for SCSS, CSS Modules, and files such as favicon.ico. I can only attest to the support for favicons, as that is all that I added to the project I used as an example in my workflow presentation/documentation.

That being said, my Jest configuration didn’t successfully mock out image import in components in testing. Result? My test for App.js, where an image was imported, failed. When I ran

npm run test

I got the following error on fail:

npm test                                                              ⏎ ✹ ✭

> text-to-speech-app@0.0.1 test /Users/mariacam/Development/text-to-speech-app
> jest

● Validation Error:

  Module custom-transformer in the transform option was not found.
         <rootDir> is: /Users/mariacam/Development/text-to-speech-app

  Configuration Documentation:

npm ERR! Test failed.  See above for more details.

A year ago, I had no need for a custom transformer or a transform option in my package.json. The "setupFiles" and "moduleNameMapper" option configurations shown here was all I needed as far as Jest was concerned. Now, however, it was looking for a custom transformer and a transform option. Why?

Because the moduleNameMapper configuration I previously used did not fulfill my (current) requirements. In that case, the following is suggested in the Jest documentation for version 23.6 entitled Using Jest With Webpack:

If moduleNameMapper cannot fulfill your requirements, you can use Jest’s transform config option to specify how assets are transformed. For example, a transformer that returns the basename of a file (such that require('logo.jpg'); returns 'logo') can be written as:

// fileTransformer.js
const path = require('path')

module.exports = {
    process(src, filename, config, options) {
        return (
            'module.exports = ' + JSON.stringify(path.basename(filename)) + ';'

I created a fileTransformer.js file in the root of my project folder where my package.json resides, and added the above code to it.

Next, according to the suggestions the same Jest documentation, Using Jest With Webpack (Jest 23.6 docs), provided, I replaced the moduleNameMapper option configuration I was using with the abridged version suggested, and added a transform option which basically picked up the rest of what previously resided in moduleNameMapper:

// package.json (for custom transformers and CSS Modules)
  "jest": {
    "moduleNameMapper": {
      "\\.(css|less|scss)$": "identity-obj-proxy"
    "transform": {
      "\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/fileTransformer.js"

Then I ran my tests again, and this time they all passed:

npm test                                                              ⏎ ✹ ✭

> text-to-speech-app@0.0.1 test /Users/mariacam/Development/text-to-speech-app
> jest

 PASS  src/sum.test.js
 PASS  src/App.test.js

Test Suites: 2 passed, 2 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        2.265s
Ran all test suites.

Advice for dealing with rapidly changing technology? Start from your point(s) of knowledge. With each error you encounter, deal with it one at a time. When I started developing projects with React 16.6.+, Webpack 4, and Babel 7, I first set up my project with my old workflow, expecting things to break, but knowing that starting from SOMEWHERE I was familiar with was going to be better than trying to start ALL over from scratch. This way, I got to a point of success much more quickly, and I learned much more. I compared the differences along the way and gained a much better understanding of how things worked both previously and now. Keeping historical records of things and building a knowledge base from them is very important.

That’s why seasoned developers who “have seen it all from the beginning” are so integral to any developer community or team! – me

To view the project structure and files associated with the project I am currently working on, and which is using the changes to the Jest configuration discussed here, please visit my Text To Speech repository.

Related Resources:

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