description: Single-page application with Blockstack
---
# Todo List
# Todos app
{:.no_toc}
In this tutorial, you build the code for and run a single-page application (SPA)
with Blockstack and React. Once the application is running, you take a tour
through the applications’ Blockstack functionality. You’ll learn how it manages
authentication using a Blockstack ID and how it stores information associated
with that ID using Blockstack Storage (Gaia).
In this tutorial, you will learn about Blockstack authentication and storage by installing, running and reviewing the code for a "Todos" web app built with Blockstack and [React](https://reactjs.org/).
This app highlights the following platform functionality:
- Generate Secret Key with associated Blockstack username to authenticate app
- Add, edit and delete encrypted app data with Gaia
- Decrypt data on Gaia for public sharing by URL
- Unauthenticate and re-authenticate app with Secret Key
[Preview the app](https://todos.blockstack.org) or [view its code on GitHub](https://github.com/blockstack/blockstack-todos).
Existing familiarity with React is recommended for reviewing this app's code.
* TOC
{:toc}
{% include note.html content="On macOS, Blockstack requires macOS High Sierra. This tutorial was written on macOS High Sierra 10.13.4. If you use a Windows or Linux system, you can still follow along. However, you will need to \"translate\" appropriately for your operating system. Additionally, this tutorial assumes you are accessing the Blockstack Browser web application via Chrome. The application you build will also work with a local installation and/or with browsers other than Chrome. " %}
### Install and run the app
## Before you begin
You must have recent versions of Git and [Node.js](https://nodejs.org/en/download/) (v12.10.0 or greater) installed already.
The application you build is a React application that is completely decentralized and server-less. While not strictly required to follow along, basic familiarity with React is helpful. When complete, the app is capable of the following:
* authenticating users using Blockstack
* posting new statuses
* displaying statuses in the user profile
* looking up the profiles and statuses of other users
1. Install the code and its dependencies:
For this tutorial, you will use the following tools:
- Node.js v10 or higher is recommended the minimum supported version is Node.js v8.
2. Run the application:
The basic identity and storage services are provided by blockstack.js. To test the application, you need to have already registered a Blockstack ID.
```bash
$ npm run start
```
You should see output similar to the following:
### Verify you have Node.js and its tools installed
```bash
Compiled successfully!
The tutorial relies on Node.js and its `npx` or `npm` tools. Before you begin, verify you have the correct version of Node.js and its tools installed.
You can now view bs-todo in the browser.
```bash
$ node -v
v12.10.0
$ which npm npx
/usr/local/bin/npm
/usr/local/bin/npx
```
http://127.0.0.1:3000/
If you don't, make sure they are installed.
Note that the development build is not optimized.
To create a production build, use npm run build.
```
### Make sure you have a Blockstack ID
2. Open your local browser to `http://localhost:3000` if it doesn't open automatically.
You should see the app's landing page:
Finally, make sure you have [created at least one Blockstack ID]({{site.baseurl}}/browser/ids-introduction.html#create-an-initial-blockstack-id).
You’ll use this ID to interact with the application.
## Task 1: Install the code and retrieve the dependencies
### Onboard into your first Blockstack app
You can clone the source code with `git` or [download and unzip the code from the repository](https://github.com/blockstack/blockstack-todos/archive/master.zip). These instructions assume you are cloning.
1. Choose **Get started** to start onboarding into the app.
The app displays a standardized introductory modal using [Blockstack Connect](https://github.com/blockstack/ux/tree/master/packages/connect), a JavaScript library that makes it easy to integrate Blockstack into the UI of any web app.
1. Install the code by cloning it.
The following [React component](https://reactjs.org/docs/react-component.html) triggers this modal in [`src/components/Signin.js`](https://github.com/blockstack/blockstack-todos/blob/master/src/components/Signin.js):
If you downloaded the zip file, the contents unzip into a `blockstack-todos-master` directory.
This component imports the [React hook](https://reactjs.org/docs/hooks-overview.html) [`useConnect`](https://github.com/blockstack/ux/blob/master/packages/connect/src/react/hooks/use-connect.ts) from the Blockstack Connect library.
`useConnect` returns many helper functions such as [`doOpenAuth`](https://github.com/blockstack/ux/blob/5934829a40338ac269b80783912c8dad17af1962/packages/connect/src/react/hooks/use-connect.ts#L33), which triggers this modal upon click of the "Get started" button.
3. Use `npm` to install the dependencies.
The modal is designed to prepare new users for a different type of relationship with Blockstack apps, one in which they authenticate with a *Secret Key* that's used to encrypt their private data.
The modal displays the app's name and icon as configured in [`src/components/App.js`](https://github.com/blockstack/blockstack-todos/blob/f6ab7b38f3f9bd98a900c7f285da4f4dd9768d60/src/components/App.js#L26):
```
$ npm install
```
The Todo application has a basic React structure. There are several configuration files but the central programming files are in the `src/components` directory:
| `components/App.js ` | Code for handling the `authResponse`. |
| `components/Signin.js ` | Code for the initial sign on page. |
| `components/Profile.js` | Application data storage and user sign out. |
```
## Task 2: Sign into the application
This component loads the [`UserSession`](https://blockstack.github.io/blockstack.js/classes/usersession.html) module from a second Blockstack library called [blockstack.js](https://github.com/blockstack/blockstack.js/), which complements Blockstack Connect by providing an API for many protocol-level operations, such as for authentication and storage.
The example application runs in a node server on your local host. In the this section, you start the application and interact with it.
```
1. Make sure you are in the root of the code base.
import { UserSession } from 'blockstack';
import { appConfig } from '../assets/constants'
```bash
$ pwd
/Users/meepers/repos/blockstack-todos
```
This path will be different for you, but double-check the last part to ensure that you're in the directory into which you cloned and in which you ran `npm install`.
...
2. Start the application in your local environment.
const userSession = new UserSession({ appConfig })
```bash
$ npm run start
```
You should see output similar to the following:
```bash
Compiled successfully!
You can now view bs-todo in the browser.
This module handles user session operations and is initiated using the [`appConfig`](https://github.com/blockstack/blockstack-todos/blob/f6ab7b38f3f9bd98a900c7f285da4f4dd9768d60/src/assets/constants.js#L3) object, which contains an array of [scopes](/develop/overview_auth.html#scopes) that indicate just what permissions to grant during authentication:
http://127.0.0.1:3000/
```
export const appConfig = new AppConfig(['store_write', 'publish_data'])
```
Note that the development build is not optimized.
To create a production build, use npm run build.
```
The `appDetails` and `userSession` objects are joined by the callback function [`finished`](https://github.com/blockstack/blockstack-todos/blob/f6ab7b38f3f9bd98a900c7f285da4f4dd9768d60/src/components/App.js#L31) in configuring Blockstack Connect for authentication with the `authOptions` object:
2. Open your local browser to the `http://localhost:3000` URL.
This function simply saves data about the user into the app's state upon authentication.
If you have already signed into Blockstack the application prompts you to select the ID to use. If you aren’t signed in, Blockstack prompts you to:
Further down in the component we see in [`componentDidMount`](https://github.com/blockstack/blockstack-todos/blob/f6ab7b38f3f9bd98a900c7f285da4f4dd9768d60/src/components/App.js#L46) that it checks upon mount to either process completion of authentication with `userSession.handlePendingSignIn()` or otherwise load session data into app state as above with `userSession.isUserSignedIn()`:
If the login to the application is successful, the user is presented with the application:
2. Choose **Get started** to generate a *Secret Key*.
## Task 3: Learn about the sign in process
The app triggers a popup window in which [the Blockstack App](https://github.com/blockstack/ux/tree/master/packages/app) is loaded from [`app.blockstack.org`](http://app.blockstack.org/) and begins generating a new *Secret Key*.
{% include sign_in.md %}
3. Choose **Copy Secret Key** to copy your *Secret Key* to the clipboard.
## Task 4: Decode the authRequest
The *Secret Key* is a unique 12-word [mnemonic phrase](https://en.bitcoinwiki.org/wiki/Mnemonic_phrase) that empowers the user not only to access Blockstack apps securely and independently. It's also used to encrypt all of the private data they create and manage with Blockstack apps.
To decode the token and see what information it holds:
*Secret Keys* are like strong passwords. However, they can never be recovered if lost or reset if stolen. As such, it's paramount that users handle them with great care.
The username will be used by the app to generate a URL for sharing your todos, should you choose to make them public.
The `iss` property is a decentralized identifier or `did`. This identifies the user and the user name to the application. The specific `did` is a `btc-addr`.
It is registered on the Stacks blockchain with the [Blockstack Naming System (BNS)](/core/naming/introduction.html) and associated with your *Secret Key*.
## Task 5: Under the covers in the sign in code
Now, go to the underlying `blockstack-todo` code you cloned or downloaded. Sign
in and sign out is handled in each of these files:
| `components/App.js ` | Code for handling the `authResponse`. |
| `components/Signin.js ` | Code for the initial sign on page. |
| `components/Profile.js` | Application data storage and user sign out. |
### Add, edit and delete todos privately
<!-- The `src/components/App.js` code configures an `AppConfig` object and then uses this to create a `UserSession`. Then, the application calls a [`redirectToSignIn()`](https://blockstack.github.io/blockstack.js#redirectToSignIn) function which generates the `authRequest` and redirects the user to the Blockstack authenticator: -->
Once you've authenticated the app, you can can start adding todos by entering values into the "Write your to do" field and hitting "Enter".
The `src/components/App.js` code configures a `UserSession` and other `authOptions`, which are passed to the `Connect` component. The `Connect` component acts as a "provider" for the rest of your application, and essentially creates a re-usable configuration for you.
In the `src/components/Signin.js` component, we are then calling the `useConnect` hook. This hook returns many helper functions, one of which is `doOpenAuth`. Calling this method will being the authentication process. First, it injects a modal into your application, which acts as a way of "warming up" your user to Blockstack authentication. When the user continues, they are redirected to the Blockstack authenticator, where they can finish signing up.
The data for all todos are saved as JSON to the Gaia hub linked to your Secret Key using the [`putFile`](http://blockstack.github.io/blockstack.js/globals.html#putfile) method of the `userSession` object in the [`src/components/Profile.js`](https://github.com/blockstack/blockstack-todos/blob/f6ab7b38f3f9bd98a900c7f285da4f4dd9768d60/src/components/Profile.js#L50) component:
Once the user authenticates, the application handles the `authResponse` in the `src/components/Profile.js` file. :
These todos are subsequently loaded using the [`getFile`](http://blockstack.github.io/blockstack.js/globals.html#getfile) method of the same object in the same component:
If [`isUserSignedIn()`](https://blockstack.github.io/blockstack.js/#isusersignedin) is true, the user was previously signed in so Blockstack pulls the data from the browser and uses it in our application. If the check on [`UserSession.isSignInPending()`](https://blockstack.github.io/blockstack.js/#issigninpending) is true, a previous `authResponse` was sent to the application but hasn't been processed yet. The `handlePendingSignIn()` function processes any pending sign in.
By default, the `putFile` and `getFile` methods automatically encrypt data when saved and decrypt it when retrieved, using the user's Secret Key. This ensures that only the user has the ability to view this data.
Signout is handled in `src/components/App.js`.
When deleting a todo, the same `putFile` method is used to save a new JSON array of todos that excludes the deleted todo.
```js
handleSignOut(e) {
e.preventDefault();
userSession.signUserOut(window.location.origin);
}
```
### Publish your todos publicly
If you wish to make your todos accessible to the public for sharing via URL, select "Make public".
The method allows the application creator to decide where to redirect the user upon Sign Out:
This will call the [`makePublic`](#) method of the `Profile.js` component, which in turn calls `saveTasks` with the `encrypt` parameter set to `false`, which is used to disable encryption when using `putFile`:
Now, trying adding a few items to the todo list. For example, try making a list of applications you want to see built on top of Blockstack:
The app will now show all of your todos to anyone who visits the URL displayed with your Blockstack username as a suffix.
Each list is immediately stored in the Gaia Hub linked to your Blockstack ID.
For more information about the Gaia hub, [see the overview in this documentation]({{ site.baseurl }}/storage/overview.html#). Now that you have seen the application in action, dig into how it works.
### Sign out and back in
## Task 7: Implement storage
Go to the underlying `blockstack-todo` code you cloned or downloaded. The application interactions with your Gaia Hub originate in the `src/components/Profile.js` file. First, examine where the changes to the Todos are processed in the `Profile.js` file.
The code needs to read the Todo items from the storage with the [`getFile()`](https://blockstack.github.io/blockstack.js/#getfile) method which returns a promise:
The `todos` data is retrieved from the promise. By default, the `getFile()` decrypts data for you. For more information on the available options, see the <ahref="https://blockstack.github.io/blockstack.js/interfaces/getfileoptions.html"taraget="_blank">the blockstack.js</a> library for details on the `GetFileOptions` interface.
During the creation of a `todos`, a JSON object is passed in and the [`putFile()`](https://blockstack.github.io/blockstack.js/#putfile) method to store it in a Gaia Hub. By default, `putFile()` encrypts data when it stores it.
You now have everything you need to construct complex applications complete with authentication and storage on the Decentralized Internet. Why not try coding [a sample application that accesses multiple profiles](blockstack_storage.html).
If you would like to explore the Blockstack APIs, you can visit the [Stacks Node API](https://core.blockstack.org/) documentation or the [Blockstack JS API](https://blockstack.github.io/blockstack.js).
The `iss` property is a decentralized identifier or `did`. This identifies the user and the user name to the application. The specific `did` is a `btc-addr`.
Mark Hendrickson
5 years ago
Hank Stoever
