为什么“npm start”不适用于全新的反应项目？

Question

我正在使用

localhost:client davea$ npm -version
6.11.3

并遵循此处的建议 -- Issue with babel-jest dependency when running npm start in a React app ，没有做任何事情来帮助我的情况。我想开始一个完全空白的项目，所以我尝试了

npx create-react-app client
cd client

但是当我尝试启动时，我得到了这个错误

localhost:client davea$ npm start

> client@0.1.0 start /Users/davea/Documents/workspace/chicommons/maps/client
> react-scripts start


There might be a problem with the project dependency tree.
It is likely not a bug in Create React App, but something you need to fix locally.

The react-scripts package provided by Create React App requires a dependency:

  "babel-jest": "^24.9.0"

Don't try to install it manually: your package manager does it automatically.
However, a different version of babel-jest was detected higher up in the tree:

  /Users/davea/Documents/workspace/node_modules/babel-jest (version: 22.4.1) 

Manually installing incompatible versions is known to cause hard-to-debug issues.

If you would prefer to ignore this check, add SKIP_PREFLIGHT_CHECK=true to an .env file in your project.
That will permanently disable this message but you might encounter other issues.

To fix the dependency tree, try following the steps below in the exact order:

  1. Delete package-lock.json (not package.json!) and/or yarn.lock in your project folder.
  2. Delete node_modules in your project folder.
  3. Remove "babel-jest" from dependencies and/or devDependencies in the package.json file in your project folder.
  4. Run npm install or yarn, depending on the package manager you use.

In most cases, this should be enough to fix the problem.
If this has not helped, there are a few other things you can try:

  5. If you used npm, install yarn (http://yarnpkg.com/) and repeat the above steps with it instead.
     This may help because npm has known issues with package hoisting which may get resolved in future versions.

  6. Check if /Users/davea/Documents/workspace/node_modules/babel-jest is outside your project directory.
     For example, you might have accidentally installed something in your home folder.

  7. Try running npm ls babel-jest in your project folder.
     This will tell you which other package (apart from the expected react-scripts) installed babel-jest.

If nothing else helps, add SKIP_PREFLIGHT_CHECK=true to an .env file in your project.
That would permanently disable this preflight check in case you want to proceed anyway.

P.S. We know this message is long but please read the steps above :-) We hope you find them helpful!

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! client@0.1.0 start: `react-scripts start`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the client@0.1.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/davea/.npm/_logs/2020-02-11T19_49_36_594Z-debug.log

我还应该做些什么来实现这个目标？

Answer 1

默认情况下create-react-app 使用 Yarn。所以我建议使用命令yarn start 来启动应用程序。由于您将使用 Yarn，因此您应该拥有 yarn.lock 文件。确保删除package-lock.json 文件（如果存在）。

最后的手段是将SKIP_PREFLIGHT_CHECK=true 添加到项目根目录中的.env 文件中。

Answer 2

我的 react js 项目没有 .env 文件，所以我创建了它并将 (SKIP_PREFLIGHT_CHECK=true) 放入其中。