firebase-admin with typescript in firebase cloud functions

It seems that types are provided when imported using ES6 Modules:

1. tsconfig.json

{
    "compilerOptions": {
        "resolveJsonModule": true,               // json imports
        "esModuleInterop": true,                 // import common modules as ES6 Modules
        "allowSyntheticDefaultImports": true,    // support typesystem compatibility
    }
}

2. index.ts

import firebase from 'firebase-admin';
import serviceAccount from './service-account.json';

const params = {               //clone json object into new object to make typescript happy
    type: serviceAccount.type,
    projectId: serviceAccount.project_id,
    privateKeyId: serviceAccount.private_key_id,
    privateKey: serviceAccount.private_key,
    clientEmail: serviceAccount.client_email,
    clientId: serviceAccount.client_id,
    authUri: serviceAccount.auth_uri,
    tokenUri: serviceAccount.token_uri,
    authProviderX509CertUrl: serviceAccount.auth_provider_x509_cert_url,
    clientC509CertUrl: serviceAccount.client_x509_cert_url
}

firebase.initializeApp({
    credential: firebase.credential.cert(params),
})

Another option could be this way.

import * as admin from 'firebase-admin';
import * as serviceAccount from './service-account.json';

const firebaseAdmin = admin.initializeApp({
   credential: admin.credential.cert(serviceAccount as admin.ServiceAccount)
});

For those who are still struggling, reloading VSCode after installing firebase-admin did the work for me.

I know i'm late but I found another way to do this, using the answer given by Peter:

1. tsconfig.json

{
    "compilerOptions": {
        "resolveJsonModule": true,               // json imports
        "esModuleInterop": true,                 // import common modules as ES6 Modules
        "allowSyntheticDefaultImports": true,    // support typesystem compatibility
    }
}

2. index.ts

import firebase from 'firebase-admin';
import serviceAccount from './service-account.json';

firebase.initializeApp({
    credential: firebase.credential.cert(serviceAccount as any), //Cast as any instead of clone the JSON.
})

import * as admin from 'firebase-admin';
const serviceAccount = require('./firebase.json');

if (!admin.apps.length) {
  admin.initializeApp({
    credential: admin.credential.cert(serviceAccount),
  });
}

export const firebaseDB = admin.firestore();