Migrating from JavaScript + Flow.js to TypeScript in Next.js 9.1.1

Question

My current project uses React.js ( 16.8.6 ) with Flow.js ( 0.109.0 ) and I want to migrate to Typescript. I am using Next.js version 9.1.1 and I don't want to change all my JS files to TS. I want to use both JS and TS files in my project. The problem is that I am using Flow.js and every time I start my development server, a typecheck error comes that says something like this -

'type aliases' can only be used in a .ts file.
     6 | import cx from 'classnames';
     7 | 
  >  8 | type Props = {
       |      ^
     9 |   heading: string,
    10 |   children: React.Node,
    11 |   headerStyles?: Object,

How should I configure my setup so that the JS files are ignored for typecheck and only TS files are considered?

My tsconfig.json files look like this -

{
  "compilerOptions": {
    "target": "es5",
    "lib": ["dom", "dom.iterable", "esnext"],
    "allowJs": true,
    "checkJs": false,
    "strict": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "noEmit": true,
    "esModuleInterop": true,
    "module": "esnext",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "jsx": "preserve"
  },
}