Installing the EsLint extension should solve your problem

if you are on VS Code, search for the EsLint extension by publisher:"Dirk Baeumer", install it and approve the installation to start the EsLint server

Alternatively run this in the terminal npm install eslint in your workspace

The package.json file gets modified and your server will be up again

for further information on the EsLint extension you can check https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint

Good luck!

in VSCode

ctrl + p
open setting.json
add this line:

  "vetur.ignoreProjectWarning": true,

this will ignore the error.

First of all, in Visual Studio code, type:

Ctrl + Shift + p

This command, will open this window

Type: settings json in search bar, like this:

Open the first option: "Open Settings (JSON)".

Now, on JSON file, add this: "vetur.ignoreProjectWarning": true, in the end of file, like this:

Restart Visual Studio Code and you're done!

Add "vetur.config.js" outside your project.

In this example below, "vetur.config.js" is added outside the project "vueProject":

Shrinking "vueProject" looks clearer:

Then, paste this code below to "vetur.config.js":

// vetur.config.js
/** @type {import('vls').VeturConfig} */
module.exports = {
  // **optional** default: `{}`
  // override vscode settings
  // Notice: It only affects the settings used by Vetur.
  settings: {
    "vetur.useWorkspaceDependencies": true,
    "vetur.experimental.templateInterpolationService": true
  },
  // **optional** default: `[{ root: './' }]`
  // support monorepos
  projects: [
    './packages/repo2', // shorthand for only root.
    {
      // **required**
      // Where is your project?
      // It is relative to `vetur.config.js`.
      root: './packages/repo1',
      // **optional** default: `'package.json'`
      // Where is `package.json` in the project?
      // We use it to determine the version of vue.
      // It is relative to root property.
      package: './package.json',
      // **optional**
      // Where is TypeScript config file in the project?
      // It is relative to root property.
      tsconfig: './tsconfig.json',
      // **optional** default: `'./.vscode/vetur/snippets'`
      // Where is vetur custom snippets folders?
      snippetFolder: './.vscode/vetur/snippets',
      // **optional** default: `[]`
      // Register globally Vue component glob.
      // If you set it, you can get completion by that components.
      // It is relative to root property.
      // Notice: It won't actually do it. You need to use `require.context` or `Vue.component`
      globalComponents: [
        './src/components/**/*.vue'
      ]
    }
  ]
}

In VS Code, if the actual code is in a subfolder (e.g you have a monorepo), you can add a vetur.config.js in the root directory as per below.

module.exports = {
    projects: [
      {
        root: './frontend', // root of your vue project (should contain package.json)
        package: './package.json', // Relative to root property, don't change this.
        tsconfig: './tsconfig.json',  // Relative to root property, don't change this.
      }
    ]
  }

Please refer to Vetur Reference for more details.