Firebase Initialization

import firebase from 'firebase/app';
import 'firebase/auth';
import 'firebase/firestore';
import 'firebase/storage';

const firebaseConfig = {
  apiKey: 'YOUR_API_KEY',
  authDomain: 'YOUR_AUTH_DOMAIN',
  projectId: 'YOUR_PROJECT_ID',
  storageBucket: 'YOUR_STORAGE_BUCKET',
  appId: 'YOUR_APP_ID',
};

firebase.initializeApp(firebaseConfig);

const auth = firebase.auth();
const db = firebase.firestore();
const storage = firebase.storage();

Authentication

// Sign up with email and password
auth.createUserWithEmailAndPassword(email, password)
  .then((userCredential) => {
    // User creation successful
    const user = userCredential.user;
  })
  .catch((error) => {
    // An error occurred
    const errorCode = error.code;
    const errorMessage = error.message;
  });

// Sign in with email and password
auth.signInWithEmailAndPassword(email, password)
  .then((userCredential) => {
    // User authentication successful
    const user = userCredential.user;
  })
  .catch((error) => {
    // An error occurred
    const errorCode = error.code;
    const errorMessage = error.message;
  });

// Sign out
auth.signOut()
  .then(() => {
    // User signed out successfully
  })
  .catch((error) => {
    // An error occurred
  });

// Get the currently signed-in user
const currentUser = auth.currentUser;

Firestore (Database)

// Get a reference to a collection
const collectionRef = db.collection('collectionName');

// Add a document to a collection
collectionRef.add({ key: 'value' })
  .then((docRef) => {
    // Document added successfully
    const documentId = docRef.id;
  })
  .catch((error) => {
    // An error occurred
  });

// Update a document
collectionRef.doc('documentId').update({ key: 'value' })
  .then(() => {
    // Document updated successfully
  })
  .catch((error) => {
    // An error occurred
  });

// Delete a document
collectionRef.doc('documentId').delete()
  .then(() => {
    // Document deleted successfully
  })
  .catch((error) => {
    // An error occurred
  });

// Get a document
collectionRef.doc('documentId').get()
  .then((doc) => {
    if (doc.exists) {
      // Document data exists
      const documentData = doc.data();
    } else {
      // Document doesn't exist
    }
  })
  .catch((error) => {
    // An error occurred
  });

// Query documents in a collection
collectionRef.where('field', '==', 'value').get()
  .then((querySnapshot) => {
    querySnapshot.forEach((doc) => {
      // Access each document
      const documentData = doc.data();
    });
  })
  .catch((error) => {
    // An error occurred
  });

Storage

// Get a reference to a file in storage
const fileRef = storage.ref().child('path/to/file.jpg');

// Upload a file
fileRef.put(file)
  .then((snapshot) => {
    // File uploaded successfully
    const downloadUrl = snapshot.downloadURL;
  })
  .catch((error) => {
    // An error occurred
  });

// Download a file
fileRef.getDownloadURL()
  .then((downloadUrl) => {
    // File download URL obtained successfully
  })
  .catch((error) => {
    // An error occurred
  });

// Delete a file
fileRef.delete()
  .then(() => {
    // File deleted successfully
  })
  .catch((error) => {
    // An error occurred
  });

This cheatsheet provides a basic overview of some common operations in Firebase.