10 minutes with Firebase

Firebase is available as both node module and browser side script.

Every data has a url

    var ref = new Firebase('https://test231.firebaseio.com/');
    rootRef = new Firebase('https://test231.firebaseio.com/');
        
    usersRef = rootRef.child('users');
    // OR
    usersRef = new Firebase("https://test231.firebaseio.com/users");
        
    // access a specific data by url
    ageRef = new Firebase("https://test231.firebaseio.com/users/mohan/age");

Write(save) data

    // set the age of mohan to 44
    ageRef.set(44);
    mohanRef = usersRef.child('mohan');
    mohanRef.set({ full_name: 'Mohan Lal', age: 50, city: 'Bengaluru' });

Update data

update() only updates data at the first child level, any data passed in beyond the first child level is a treated as a set() operation.

    mohanRef.update({ job: 'WeeWee' });
    // { full_name: 'Mohan Lal', age: 50, city: 'Bengaluru', job: 'WeeWee' }

Write and Update using callbacks

    someRef.set('this is a message', function( err ) {
         if(!err) {
              console.log('Data was updated successfully!');
         }
    });

Push data

At a multi user platform where simultaneously several users are engaging with the same data, the use of set() might be hazardous. Instead firebase provides push() that generates a unique ID every time a new child is added to the specified database reference.

        var postsRef = ref.child("posts");

        // `push()` returns the ref to the newly added data 
        var refMohanPost = postsRef.push({
             author: "mohan",
             title: "How to swim in an empty pond"
        });

        var refLilyPost = postsRef.push({
            author: "lily",
             title: "You smell like pie"
        });

        // get the unique ID generated
        var mohanPostId = refMohanPost.key();

Transaction

These are useful for “atomic operations”

    // Atomically incrementing an upvote

    var upvoteRef = new Firebase(' ... upvote data url ... ');
    upvoteRef.transaction(function (current_value) {
         return (current_value || 0) + 1;
    });


    // Try to create a user for mohan, but only if the user id 'mohan' isn't already taken

    var mohanRef = new Firebase('https://test231.firebaseio.com/users/mohan');
    mohanRef.transaction(function(currentData) {
 
    if (currentData === null) {
             console.log('User mohan does not exist therefore we can create it.');
             return { full_name: 'Mohan Lal', age: 50, city: 'Bengaluru' };
         } else {
             console.log('User mohan already exists.');
             return; // Abort the transaction i.e. Don't return anything
         }
    }, function(error, committed, snapshot) {
     
          if (error) {
             console.log('Transaction failed abnormally!', error);
         } else if (!committed) {
             console.log('We aborted the transaction (because mohan already exists).');
         } else {
             console.log('User mohan added!');
         }

         console.log("Wilma's data: ", snapshot.val());

    });

Offline

A firebase client also maintains its own local version of it, so everytime it is written to this local version first and then client then synchronizes the local version with the database. Once connectivity is reestablished, firebase database will receive the appropriate set of events so that the client “catches up” with the current server state.

Read data

    usersRef = new Firebase("https://test231.firebaseio.com/users");

    // returns the entire users array 
    usersRef.on('value', function(snapshot) {
         console.log( snapshot.val() );  // array
    }, function(err) {
         console.log('Looks like you do not have permission to READ.');
    });

    // returns the added `child` 
    usersRef.on('child_added', function(snapshot) {
         console.log( snapshot.val() );  // array element
    }, function(err) {
         console.log('Looks like you do not have permission to READ.');
    });

And similarly, child_changed and child_removed.

once()

    firebaseRef.once('value', function (snapshot) {
        // code to handle new value
    }, function (err) {
        // code to handle read error
    });

Security Check!

Below example allows anyone to read/write /users/mohan and its children, but doesn’t allow for admin.

Config

    {
         "rules": {
             "users": {
                 "admin": {
                     ".read": false,
                     ".write": false
                 },
                 "mohan": {
                     ".read": true,
                     ".write": true
                  }
             }
         }
    }

Authenticate with a token

    usersRef = new Firebase("https://test231.firebaseio.com/users");
    usersRef.authWithCustomToken("MY_AUTH_TOKEN", function(error, authData) {
        if (error) {
            console.log("Authentication Failed!", error);
        } else {
            console.log("Authenticated successfully with payload:", authData);
        }
    });

How to check if user is authenticated or not?

    var authData = usersRef.getAuth();
    if (authData) {
         console.log("Authenticated!");
    }

A few pieces of API

    // Parent
    var parentRef = usersRef.parent();   // https://test231.firebaseio.com

    // Root
    var rootRef = usersRef.root();   // https://test231.firebaseio.com

Check out more

Docs
API