必需的babel-jest依赖性

Question

I am new in the topic of React. I started it recently and I have a problem when I want to start a React app. 'yarn start' shows this error:

The react-scripts package provided by Create React App requires a dependency: "babel-jest": "23.6.0" 

How can I overcome this error, please.

I tried to find a solution on Internet but I was not lucky. Where is the problem, please?

Answer 1

So it looks like what might have happened was that after you created a new app using create-react-app . you then manually added the babel-jest package with yarn add babel-jest . At least, that's how I was able to replicate on my machine the error that you quoted.

You do not need to add the babel-jest package manually, as it is already bundled into create-react-app . So, you need to follow the instructions that were provided alongside the above error in order to remove the package:

First, open package.json and remove the dependency line that includes babel-jest . It might look something like this:

// package.json
{
  "name": "babel",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "babel-jest": "23.6.0",  <----------- REMOVE THIS LINE
    "react": "^16.8.4",
    "react-dom": "^16.8.4",
    "react-scripts": "2.1.8"
  },

Then, since you're using yarn , do the following from within your project root folder:

rm -rf node_modules
rm yarn.lock
yarn install

This removes the manually added babel-jest package and then gives you a fresh install of all of the packages that originally came with create-react-app (which includes the babel-jest package that is already bundled in).

---

Update

Based on your comment, I believe that has happened is this:

1. You used npm init which initialized a new nodejs project, with its own package.json file.

2. Then in that folder, you used create-react-app to create a test sub-folder - this initialized another project with its own package.json file.

3. For some reason, the project in the parent folder (which you initialized with npm init ) has a reference to babel-jest - and this is conflicting with the app in the child folder which you created with create-react-app .

Keep in mind that npm and yarn are both package managers for nodejs projects. Each of them have an init command which can be used to initialize a new project, setting up a package.json file. For the most part, you will never need to use both npm and yarn within a single project. Just choose which one you want to use and stick with that one.

create-react-app is another command which can be used to initialize a new ReactJS project with a lot of initial setup built in. This has babel-jest built into it, which is what might be leading to some conflicts with the parent folder's package.json file or possibly a globally installed babel-jest package.

As a general rule, you should only use 1 of the following: * npm init initializes a project at the current folder. * yarn init initializes a project at the current folder. * create-react-app . initializes a project at the current folder.

For your current situation, since you are working with a new project, I would recommend that you try to start over in initializing a new create-react-app project. Go to the parent folder, outside of the one where you used the npm init command. Create a project folder, and then in that folder, run create-react-app .