Next.js Internet Computer Starter Template

Note: If you run it in MacOS, you may be asked to allow connections from dfx local server.

Enter the commands to install dependencies, deploy canister and run Next.js dev server:

npm install
dfx deploy
npm run dev

http://localhost:3000/

Cleanup - stop dfx server running in background:

dfx stop

Project Structure

Internet Computer has the concept of Canister which is a computation unit. This project has 3 canisters:

• hello (backend)
• image (backend)
• hello_assets (frontend)

Canister configurations are stored in dfx.json.

Backend

Backend code is inside /backend/ written in Motoko language. Motoko is a type-safe language with modern language features like async/await and actor build-in. It also has Orthogonal persistence which I find very interesting.

Image canister is introduced from release v0.2.0. It makes use of orthogonal persistence through stable variables and provides functions for create, delete and get image. See /backend/service/Image.mo.

Frontend

Frontend code follows Next.js folder convention with /pages storing page React code, /public storing static files including images. This project uses CSS modules for styling which is stored in /ui/styles. React Components are stored in /ui/components

Entry page code is inside /pages/index.js where the magic starts. With the DFX UI declarations generated code, frontend can use RPC style call to server side actor and its functions without worrying about HTTP request and response parsing.

To generate UI declarations:

dfx generate

It will generate files in src/declarations for each canister. In our case, it is image, hello and hello_assets but we only need the backend canister image and hello UI declarations here.

The next step is to adapt it to work with Next.js. The final adapted code is in ui/declaration/hello/index.js. You can also follow the steps below to update it.

Basically, copy image.did.js and index.js from src/declarations/image/

cp src/declarations/image/image.did.js ui/declarations/image/image.did.js
cp src/declarations/image/index.js ui/declarations/image/index.js

Repeat the same for hello.

cp src/declarations/hello/hello.did.js ui/declarations/hello/hello.did.js
cp src/declarations/hello/index.js ui/declarations/hello/index.js

The next step is to update the canister ID env variable in each canister index.js to use NEXT_PUBLIC prefix so that NextJS can recognize when compiling it.

Open ui/declarations/hello/index.js and look for the line:

export const canisterId = process.env.HELLO_CANISTER_ID;

Update HELLO_CANISTER_ID to NEXT_PUBLIC_HELLO_CANISTER_ID:

export const canisterId = process.env.NEXT_PUBLIC_HELLO_CANISTER_ID

To see the final code, check the original ui/declarations in the Git repo.

The generated UI declarations also support TypeScript if you prefer TypeScript.

We use a service locator pattern through actor-locator.js that will handle the dfx agent host using env var NEXT_PUBLIC_IC_HOST.

Creating hello actor:

import { makeHelloActor } from "../ui/service/actor-adapter"
const hello = makeHelloActor()

Calling hello actor:

const greeting = await hello.greet(name)

The beautiful part is you can invoke the hello actor greet function with async/await style as if they are on the same platform. For details, see React Components GreetingSection.js and ImageSection.js in /ui/components/.

Webpack configuration:
In Next.js, it's located in next.config.js.

React Hook

By using React Hook with actor UI declaration, it can greatly simplify frontend dev. It encourages component based composable logic. A great example is useImageObject.js React Hook in /ui/hooks. Given an imageId, useImageObject can load the image binary and convert it to a HTML image source object ready for use in .

If you look closer, useImageObject.js depends on image-serivce.js which depends on actor-locator.js. When you open ImageSection.js, you can find how useImageObject is being used to greatly reduce the complexity and the underlying calls with Canister. This is the pattern I used very often in my Content Fly Dapp project.

Backend dev

After marking changes in backend code e.g main.mo in /backend/service/hello, you can deploy it to the local DFX server using:

dfx deploy hello

hello is the backend canister name defined in dfx.json.

Frontend dev - Next.js Static Code

Next.js developers are familiar with the handy hot code deployed in the Next.js dev environment when making changes in frontend code.

After deploying your backend code as shown above, you can run Next.js local dev server npm run dev and edit your frontend code with all the benefits of hot code deploy.

One thing to note is we use Next.js static code export here for hosting in Internet Computer so we can't use any features of Next.js that require server side NodeJS. Potentially, there might be ways to use Internet Computer canister as backend while deploying Next.js dapp to a hosting like Vercel that supports NodeJS server in the future. Further research is needed on that aspect. However, if you do want to run everything decentralized on blockchain including the frontend, you would want to deploy the exported static code to Internet Computer as well.

Deploy and run frontend in local DFX server

In order to simulate the whole Internet Computer experience, you can deploy and run frontend code to local DFX server by running:

dfx start --background
npm run build
dfx deploy hello_assets

hello_assets is the frontend canister defined in dfx.json.

npm run build builds and export Next.js as static code storing in /out folder which would be picked up by dfx deploy hello_assets as defined in dfx.json with /out as the source.

When it completes, you can open Chrome and browse to:
http://localhost:8000/?canisterId=[canisterId]

Replace [canisterId] with the hello_assets canister ID which you can find by running:

dfx canister id hello_assets

Environment Configuration

There are three key configs following Next.js Environment Variables configuration:

.env.development stores configs for use in local dev.

NEXT_PUBLIC_IC_HOST=http://localhost:8000

.env.production is used when building and exporting static code using npm run build

NEXT_PUBLIC_IC_HOST=http://localhost:8000

Notice both files are identical if we want the Next.js dapp to interact with the local dfx server.

Note NEXT_PUBLIC is the prefix used by Next.js to make env vars available to client side code through build time inlining.

.env.icprod is included for deployment to Internet Computer ic network which would be covered below.

Deploy to IC Network Canister

The most exciting part is to deploy your Next.js / Internet Computer Dapp to production Internet Computer mainnet blockchain network.

To do that you will need:

• ICP tokens and convert it to cycles
• Cycles wallet

Follow the Network Deployment guide to create a wallet.
Dfinity offers free cycle to developers.

Now, you can deploy your Next.js Dapp to Internet Computer IC network by adding --network ic to the dfx subcommand. We will first update our env var to point to IC network host. Then deploy the backend canister first, export Next.js static code and deploy frontend canister hello_assets.

cp .env.icprod .env.production
dfx deploy --network ic

Open Chrome and go to https://[canisterId].raw.ic0.app/
Replace [canisterId] by the hello_assets canister id in the IC network. You can find it by running:

dfx canister --network ic id hello_assets

Congratulations !! Well Done !! 👏 🚀 🎉

Troubleshooting

Use Chrome Dev Tools / Console / Network. Check if the dapp uses the right canister id and hostname.

Author

Henry Chan, henry@contentfly.app Twitter: @kinwo

Contributing

Please feel free to raise an issue or submit a pull request.

License

MIT