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Count on NEAR

Our counter example is a friendly decentralized app that stores a number and exposes methods to increment, decrement, and reset it.

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Starting the Counter​

You have two options to start the Counter:

  1. Recommended: use the app through Gitpod (a web-based interactive environment)
  2. Clone the project locally .
GitpodClone locally
Open in Gitpod🌐 https://github.com/near-examples/js-counter.git

If you choose Gitpod, a new browser window will open automatically with the code. Give it a minute, and the frontend will pop up (ensure the pop-up window is not blocked).

If you are running the app locally, enter the directory where you cloned it and use yarn to install dependencies, and yarn start to start it.

cd counter
yarn
yarn deploy
yarn start

Your contract will then be compiled and deployed to an account in the testnet network. When done, a browser window should open.

Interacting With the Counter​

Go ahead and login with your NEAR account. If you don't have one, you will be able to create one in the moment. Once logged in, use the + and - buttons to increase and decrease the counter. Then, use the Gameboy buttons to reset it and make the counter blink an eye!

img Frontend of the Counter

Structure of a dApp​

Now that you understand what the dApp does, let us take a closer look to its structure:

  1. The frontend code lives in the /frontend folder.
  2. The smart contract code is in the /contract folder.

Contract​

The contract presents 4 methods: get_num, increment, decrement, and reset. The method get_num retrieves the current value, and the rest modify it.

contract/src/contract.ts
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Frontend​

The frontend is composed by a single HTML file (/index.html). This file defines the components displayed in the screen.

The website's logic lives in /assets/js/index.js, which communicates with the contract through /near-interface.js. You will notice in /assets/js/index.js the following code:

frontend/index.js
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It indicates our app, when it starts, to check if the user is already logged in and execute either signedInFlow() or signedOutFlow().

Testing​

When writing smart contracts it is very important to test all methods exhaustively. In this project you have two types of tests: unit and integration. Before digging in them, go ahead and perform the tests present in the dApp through the command yarn test.

Unit test​

Unit tests check individual functions in the smart contract. Right now only Rust implements unit testing.

contract/src/lib.rs
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Integration test​

Integration tests are generally written in javascript. They automatically deploy a new contract and execute methods on it. In this way, integration tests simulate interactions from users in a realistic scenario. You will find the integration tests for the counter in tests/integration-tests.

integration-tests/src/main.ava.ts
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Moving Forward​

A nice way to learn is by trying to expand the contract. Modify it by adding a parameter to increment and decrement, so the user can choose by how much to change the value. For this, you will need to use knowledge from the anatomy and storage sections.