Delete Firestore Collection using firebase function

I am trying to set up a firebase function that deletes all subcollections of a document when the document is deleted. Trough reading the documentation I have come to this code:

// The Cloud Functions for Firebase SDK to create Cloud Functions and setup triggers.
const functions = require('firebase-functions');



// // Create and Deploy Your First Cloud Functions
// // https://firebase.google.com/docs/functions/write-firebase-functions
//
// exports.helloWorld = functions.https.onRequest((request, response) => {
//  response.send("Hello from Firebase!");
// });

exports.DeleteColletionFunction = functions.firestore
    .document('exampleCollection/{exampleID}')
    .onDelete((snap, context) => {
        // Get an object representing the document prior to deletion
      // e.g. {'name': 'Marie', 'age': 66}
      const deletedValue = snap.data();
      deleteCollection()


    });



function deleteCollection(db, collectionPath, batchSize) {
    var collectionRef = db.collection(collectionPath);
    var query = collectionRef.orderBy('__name__').limit(batchSize);

    return new Promise((resolve, reject) => {
      deleteQueryBatch(db, query, batchSize, resolve, reject);
    });
  }

  function deleteQueryBatch(db, query, batchSize, resolve, reject) {
    query.get()
        .then((snapshot) => {
          // When there are no documents left, we are done
          if (snapshot.size == 0) {
            return 0;
          }

          // Delete documents in a batch
          var batch = db.batch();
          snapshot.docs.forEach((doc) => {
            batch.delete(doc.ref);
          });

          return batch.commit().then(() => {
            return snapshot.size;
          });
        }).then((numDeleted) => {
          if (numDeleted === 0) {
            resolve();
            return;
          }

          // Recurse on the next process tick, to avoid
          // exploding the stack.
          process.nextTick(() => {
            deleteQueryBatch(db, query, batchSize, resolve, reject);
          });
        })
        .catch(reject);
  }

I have never worked before with cloud functions and therefore am not sure what I should do next. I see that in order to use the delete Collection function it is necessary to pass a database, collectionPath and batchSize. What would be the right values to pass in this case?

Should I use this line of code to get the firestore database?

const database = admin.firestore();

I am also getting some errors when copying this function from the documentation:

Expected '===' and instead saw '=='

[eslint] Avoid nesting promises. (promise/no-nesting) (parameter) snapshot: any

[eslint] Each then() should return a value or throw (promise/always-return) (parameter) resolve: any

Here is a screenshot to see the locations of the errors:

Thank you for your help!

UPDATE:
I changed some things (adding a promise):

// The Cloud Functions for Firebase SDK to create Cloud Functions and setup triggers.
const functions = require('firebase-functions');

const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);


// // Create and Deploy Your First Cloud Functions
// // https://firebase.google.com/docs/functions/write-firebase-functions
//
// exports.helloWorld = functions.https.onRequest((request, response) => {
//  response.send("Hello from Firebase!");
// });

exports.DeleteColletionFunction = functions.firestore
    .document('exampleCollection/{exampleID}')
    .onDelete((snap, context) => {
        // Get an object representing the document prior to deletion
      // e.g. {'name': 'Marie', 'age': 66}
      const deletedValue = snap.data();
      const exampleID = context.params.exampleID;

      const BATCH_SIZE = 500;

      const database = admin.firestore();

      const commentsRef = database.collection('exampleCollection').doc(exampleID).collection("comments");

      commentsRef.doc('main').delete();

      const exampleRef = database.collection('exampleCollection').doc(exampleID).collection("exampleSubCollection");
      const deleteExamples = deleteCollection(database, exampleRef, BATCH_SIZE)
      return Promise.all([deleteExamples]);

   });



/**
 * Delete a collection, in batches of batchSize. Note that this does
 * not recursively delete subcollections of documents in the collection
 */
function deleteCollection (db, collectionRef, batchSize) {
    var query = collectionRef.orderBy('__name__').limit(batchSize)

    return new Promise(function (resolve, reject) {
      deleteQueryBatch(db, query, batchSize, resolve, reject)
    })
  }

  function deleteQueryBatch (db, query, batchSize, resolve, reject) {
    query.get()
.then((snapshot) => {
        // When there are no documents left, we are done
        if (snapshot.size === 0) {
          return 0
        }

      // Delete documents in a batch
      var batch = db.batch()
      snapshot.docs.forEach(function (doc) {
        batch.delete(doc.ref)
      })

      return batch.commit().then(function () {
        return snapshot.size
      })
    }).then(function (numDeleted) {
      if (numDeleted <= batchSize) {
        resolve()
        return
      }
      else {
      // Recurse on the next process tick, to avoid
      // exploding the stack.
      return process.nextTick(function () {
        deleteQueryBatch(db, query, batchSize, resolve, reject)
      })
    }
  })
    .catch(reject)
  }

Now I am getting errors in the firebase console:

ReferenceError: exampleID is not defined at exports.DeleteColletionFunction.functions.firestore.document.onDelete (/user_code/index.js:26:66) at Object. (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:112:27) at next (native) at /user_code/node_modules/firebase-functions/lib/cloud-functions.js:28:71 at __awaiter (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:24:12) at cloudFunction (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:82:36) at /var/tmp/worker/worker.js:728:24 at process._tickDomainCallback (internal/process/next_tick.js:135:7)

Thanks for your help!