Use Typescript to check JavaScript

jsconfig.json

// add this file to the root of your repo without these comment lines
// inside `compilerOptions`, include "moduleResolution": "node" if it's a Node project
// remove `jsx` lines if not using JSX
{
  "compilerOptions": {
    "target": "es2017",
    "checkJs": true,
    "jsx": "react"
  },
  "include": [
    "src/**/*.js",
    "src/**/*.jsx"
  ],
  "exclude": [
    "node_modules"
  ]
}