# Connection Process The connection process for PAPI follows a structured workflow that ensures your application can both connect to and interact with the Polkadot network. Here’s a step-by-step explanation: ### 1. Provider Setup The first step in connecting to a chain is creating a provider, which acts as a communication bridge between your application and the blockchain. PAPI offers multiple ways to establish this connection, such as using: - **getWsProvider (the WebSocket Provider)**: Connects via a WebSocket URL, often used for real-time interactions. - **Smoldot Provider**: A lightweight option that runs a light client in the browser, particularly useful for environments with limited resources. In your app, you would initialize the provider like this: ```ts import { getWsProvider } from "polkadot-api/ws-provider/web"; ... const provider = new getWsProvider('wss://rpc.polkadot.io'); ``` ### 2. Client Initialization After setting up the provider, the next step is to initialize a **client**. The client is responsible for making RPC calls to the chain, fetching metadata, and enabling interactions like querying storage or sending transactions. ```ts import { createClient, type PolkadotClient } from "polkadot-api"; ... const client: PolkadotClient = createClient(provider); ``` The `PolkadotClient` interface shapes the top-level API for polkadot-api. Once we get a client using `createClient` function, the following can be used: ```ts interface PolkadotClient { /** * Retrieve the ChainSpecData as it comes from the [JSON-RPC * spec](https://paritytech.github.io/json-rpc-interface-spec/api/chainSpec.html) */ getChainSpecData: () => Promise; /** * Observable that emits `BlockInfo` from the latest known finalized block. * It's a multicast and stateful observable, that will synchronously replay * its latest known state. */ finalizedBlock$: Observable; /** * @returns Latest known finalized block. */ getFinalizedBlock: () => Promise; /** * Observable that emits an Array of `BlockInfo`, being the first element the * latest known best block, and the last element the latest known finalized * block. It's a multicast and stateful observable, that will synchronously * replay its latest known state. This array is an immutable data structure; * i.e. a new array is emitted at every event but the reference to its * children are stable if the children didn't change. * * Note that subscribing to this observable already supersedes the need of * subscribing to `finalizedBlock$`, since the last element of the array will * be the latest known finalized block. */ bestBlocks$: Observable; /** * @returns Array of `BlockInfo`, being the first element the latest * known best block, and the last element the latest known * finalized block. */ getBestBlocks: () => Promise; /** * Observable to watch Block Body. * * @param hash It can be a block hash, `"finalized"`, or `"best"` * @returns Observable to watch a block body. There'll be just one event * with the payload and the observable will complete. */ watchBlockBody: (hash: string) => Observable; /** * Get Block Body (Promise-based) * * @param hash It can be a block hash, `"finalized"`, or `"best"` * @returns Block body. */ getBlockBody: (hash: string) => Promise; /** * Get Block Header (Promise-based) * * @param hash It can be a block hash, `"finalized"` (default), or * `"best"` * @returns Block hash. */ getBlockHeader: (hash?: string) => Promise; /** * Broadcast a transaction (Promise-based) * * @param transaction SCALE-encoded tx to broadcast. * @param at It can be a block hash, `"finalized"`, or `"best"`. * That block will be used to verify the validity of * the tx, retrieve the next nonce, * and create the mortality taking that block into * account. */ submit: ( transaction: HexString, at?: HexString, ) => Promise; /** * Broadcast a transaction and returns an Observable. The observable will * complete as soon as the transaction is in a finalized block. * * @param transaction SCALE-encoded tx to broadcast. * @param at It can be a block hash, `"finalized"`, or `"best"`. * That block will be used to verify the validity of * the tx, retrieve the next nonce, * and create the mortality taking that block into * account. */ submitAndWatch: ( transaction: HexString, at?: HexString, ) => Observable; /** * Returns an instance of a `TypedApi` * * @param descriptors Pass descriptors from `@polkadot-api/descriptors` * generated by `papi` CLI. */ getTypedApi: (descriptors: D) => TypedApi; /** * This will `unfollow` the provider, disconnect and error every subscription. * After calling it nothing can be done with the client. */ destroy: () => void; /** * This API is meant as an "escape hatch" to allow access to debug endpoints * such as `system_version`, and other useful endpoints that are not spec * compliant. * * @example * * const systemVersion = await client._request("system_version", []) * const myFancyThhing = await client._request< * { value: string }, * [id: number] * >("very_fancy", [1714]) * */ _request: = any[]>( method: string, params: Params, ) => Promise; } ``` > Note: `PolkadotClient` heavily relies on rxjs' `Observable`, used as well under the hood of Promise-based methods. Every method is fairly straight-forward and already documented exhaustively, except for getTypedApi. Let's dive into it. > > Information from: https://papi.how/client

Polkadot API: An Introduction to multi-chain

Skill Level

Beginner

Time to Complete

1 hour

Course Content

1 section

Prerequisites

None

About This Course

What You'll Learn

Course Content

Introduction to the new Polkadot API