第四课作业 -- 使用 js sdk 从浏览器 frontend 获取到前面写入 Offchain Storage 的数据

使用 js sdk 从浏览器 frontend 获取到前面写入 Offchain Storage 的数据、在pallet-template 中增加storeToOffchainStorage的extrinsic，使用offchain worker读出后调用do_something提交交易至链上，重用template的界面显示数据

pallet kitty 第三课作业--小毛孩的UI

gif截图如下：

Substrate Front End Template

This template allows you to create a front-end application that connects to a Substrate node back-end with minimal configuration. To learn about Substrate itself, visit the Substrate Documentation.

The template is built with Create React App and Polkadot js API. Familiarity with these tools will be helpful, but the template strives to be self-explanatory.

Using The Template

Installation

The codebase is installed using git and yarn. This tutorial assumes you have installed yarn globally prior to installing it within the subdirectories. For the most recent version and how to install yarn, please refer to Yarn documentation and installation guides.

# Clone the repository
git clone https://github.com/substrate-developer-hub/substrate-front-end-template.git
cd substrate-front-end-template
yarn install

Usage

You can start the template in development mode to connect to a locally running node

yarn start

You can also build the app in production mode,

yarn build

and open build/index.html in your favorite browser.

Try the Hosted Version

Connecting to Polkadot:
https://substrate-developer-hub.github.io/substrate-front-end-template?rpc=wss://rpc.polkadot.io

Connecting to your local Substrate node (Chrome and Firefox only):
https://substrate-developer-hub.github.io/substrate-front-end-template?rpc=ws://localhost:9944

Connecting to the development Substrate node wss://dev-node.substrate.dev:
https://substrate-developer-hub.github.io/substrate-front-end-template

Configuration

The template's configuration is stored in the src/config directory, with common.json being loaded first, then the environment-specific json file, and finally environment variables, with precedence.

development.json affects the development environment
test.json affects the test environment, triggered in yarn test command.
production.json affects the production environment, triggered in yarn build command.

Some environment variables are read and integrated in the template config object, including:

REACT_APP_PROVIDER_SOCKET overriding config[PROVIDER_SOCKET]

Specifying Connecting WebSocket

There are two ways to specify it:

With PROVIDER_SOCKET in {common, development, production}.json.
With rpc=<ws or wss connection> query parameter after the URL. This overrides the above setting.

Reusable Components

useSubstrate Custom Hook

The custom hook useSubstrate() provides access to the Polkadot js API and thus the keyring and the blockchain itself. Specifically it exposes this API.

{
  setCurrentAccount: func(acct) {...}
  state: {
    socket,
    keyring,
    keyringState,
    api,
    apiState,
    currentAccount
  }
}

socket - The remote provider socket it is connecting to.
keyring - A keyring of accounts available to the user.
keyringState - One of "READY" or "ERROR" states. keyring is valid only when keyringState === "READY".
api - The remote api to the connected node.
apiState - One of "CONNECTING", "READY", or "ERROR" states. api is valid only when apiState === "READY".
currentAccount - The current selected account pair in the application context.
setCurrentAccount - Function to update the currentAccount value in the application context.

If you are only interested in reading the state, there is a shorthand useSubstrateState() just to retrieve the state.

TxButton Component

The TxButton handles basic query and transaction requests to the connected node. You can reuse this component for a wide variety of queries and transactions. See src/Transfer.js for a transaction example and src/Balances.js for a query example.

Account Selector

The Account Selector provides the user with a unified way to select their account from a keyring. If the Balances module is installed in the runtime, it also displays the user's token balance. It is included in the template already.

Miscellaneous

Polkadot-js API and related crypto libraries depend on BigInt that is only supported by modern browsers. To ensure that react-scripts properly transpile your webapp code, update the package.json file:
```
{
  "browserslist": {
    "production": [
      ">0.2%",
      "not ie <= 99",
      "not android <= 4.4.4",
      "not dead",
      "not op_mini all"
    ]
  }
}
```
Refer to this doc page.

tomxiong/advance-5