@polkadot/api/promise

Overview

name: ApiPromise

description: ApiPromise is a standard JavaScript wrapper around the RPC and interfaces on the Polkadot network. As a full Promise-based, all interface calls return Promises, including the static .create(...). Subscription calls utilise (value) => {} callbacks to pass through the latest values.

The API is well suited to real-time applications where either the single-shot state is needed or use is to be made of the subscription-based features of Polkadot (and Substrate) clients.

see: ApiRx

Usage

Making rpc calls -

import ApiPromise from '@polkadot/api/promise';

// initialise via static create
const api = await ApiPromise.create();

// make a subscription to the network head
api.rpc.chain.subscribeNewHead((header) => {
  console.log(`Chain is at #${header.blockNumber}`);
});

Subscribing to chain state -

import { ApiPromise } from '@polkadot/api';
import WsProvider from '@polkadot/rpc-provider/ws';

// initialise a provider with a specific endpoint
const provider = new WsProvider('wss://example.com:9944')

// initialise via isReady & new with specific provider
const api = await new ApiPromise(provider).isReady;

// retrieve the block target time
const blockPeriod = await api.query.timestamp.blockPeriod().toNumber();
let last = 0;

// subscribe to the current block timestamp, updates automatically (callback provided)
api.query.timestamp.now((timestamp) => {
  const elapsed = last
    ? `, ${timestamp.toNumber() - last}s since last`
    : '';

  last = timestamp.toNumber();
  console.log(`timestamp ${timestamp}${elapsed} (${blockPeriod}s target)`);
});

Submitting a transaction -

import ApiPromise from '@polkadot/api/promise';

ApiPromise.create().then((api) => {
  const nonce = await api.query.system.accountNonce(keyring.alice.address());

  api.tx.balances
    // create transfer
    transfer(keyring.bob.address(), 12345)
    // sign the transcation
    .sign(keyring.alice, nonce)
    // send the transaction (optional status callback)
    .send((status) => {
      console.log(`current status ${status.type}`);
    })
    // retrieve the submitted extrinsic hash
    .then((hash) => {
      console.log(`submitted with hash ${hash}`);
    });
});

Hierarchy

ApiBase<DecoratedRpc, QueryableStorage, SubmittableExtrinsics>

↳ ApiPromise

Implements

• ApiBaseInterface<DecoratedRpc, QueryableStorage, SubmittableExtrinsics>
• ApiPromiseInterface

Constructors

constructor

⊕ new ApiPromise(options?: ApiOptions | ProviderInterface): ApiPromise

Overrides ApiBase.constructor

Defined in promise/index.ts:137

description: Creates an instance of the ApiPromise class

example:

import Api from '@polkadot/api/promise';

new Api().isReady.then((api) => {
  api.rpc.subscribeNewHead((header) => {
    console.log(`new block #${header.blockNumber.toNumber()}`);
  });
});

Parameters:

Returns: ApiPromise

Accessors

genesisHash

getgenesisHash(): Hash

Inherited from ApiBase.genesisHash

Defined in Base.ts:77

description: Contains the genesis Hash of the attached chain. Apart from being useful to determine the actual chain, it can also be used to sign immortal transactions.

Returns: Hash

hasSubscriptions

gethasSubscriptions(): boolean

Inherited from ApiBase.hasSubscriptions

Defined in Base.ts:86

description: true when subscriptions are supported

Returns: boolean

isReady

getisReady(): Promise<ApiPromise>

Defined in promise/index.ts:172

description: Promise that returns the first time we are connected and loaded

Returns: Promise<ApiPromise>

query

getquery(): QueryableStorage

Inherited from ApiBase.query

Defined in Base.ts:122

description: Contains all the chain state modules and their subsequent methods in the API. These are attached dynamically from the runtime metadata.

All calls inside the namespace, is denoted by section.method and may take an optional query parameter. As an example, api.query.timestamp.now() (current block timestamp) does not take parameters, while api.query.system.accountNonce(<accountId>) (retrieving the associated nonce for an account), takes the AccountId as a parameter.

example:

api.query.balances.freeBalance(<accountId>, (balance) => {
  console.log('new balance', balance);
});

Returns: QueryableStorage

rpc

getrpc(): DecoratedRpc

Inherited from ApiBase.rpc

Defined in Base.ts:142

description: Contains all the raw rpc sections and their subsequent methods in the API as defined by the jsonrpc interface definitions. Unlike the dynamic api.query and api.tx sections, these methods are fixed (although extensible with node upgrades) and not determined by the runtime.

RPC endpoints available here allow for the query of chain, node and system information, in addition to providing interfaces for the raw queries of state (usine known keys) and the submission of transactions.

example:

api.rpc.chain.subscribeNewHead((header) => {
  console.log('new header', header);
});

Returns: DecoratedRpc

runtimeMetadata

getruntimeMetadata(): Metadata

Inherited from ApiBase.runtimeMetadata

Defined in Base.ts:93

description: Yields the current attached runtime metadata. Generally this is only used to construct extrinsics & storage, but is useful for current runtime inspection.

Returns: Metadata

runtimeVersion

getruntimeVersion(): RuntimeVersion

Inherited from ApiBase.runtimeVersion

Defined in Base.ts:102

description: Contains the version information for the current runtime.

Returns: RuntimeVersion

tx

gettx(): SubmittableExtrinsics

Inherited from ApiBase.tx

Defined in Base.ts:161

description: Contains all the extrinsic modules and their subsequent methods in the API. It allows for the construction of transactions and the submission thereof. These are attached dynamically from the runtime metadata.

example:

api.tx.balances
  .transfer(<recipientId>, <balance>)
  .sign(<keyPair>, <accountNonce>, <blockHash (optional)>)
  .send((status) => {
    console.log('tx status', status);
  });

Returns: SubmittableExtrinsics

Methods

combineLatest

▸ combineLatest(fns: Array<CombinatorFunction | [CombinatorFunction, Array]>, callback: CombinatorCallback): PromiseSubscription

Defined in promise/index.ts:255

description: Creates a combinator that can be used to combine the latest results from multiple subscriptions

example:

const address = '5DTestUPts3kjeXSTMyerHihn1uwMfLj8vU8sqF7qYrFacT7';

// combines values from balance & nonce as it updates
api.combineLatest([
  api.rpc.chain.subscribeNewHead,
  [api.query.balances.freeBalance, address],
  (cb) => api.query.system.accountNonce(address, cb)
], ([head, balance, nonce]) => {
  console.log(`#${head.number}: You have ${balance} units, with ${nonce} transactions sent`);
});

Parameters:

Returns: PromiseSubscription

on

▸ on(type: ApiInterface$Events, handler: function): this

Inherited from ApiBase.on

Defined in Base.ts:186

description: Attach an eventemitter handler to listen to a specific event

example:

api.on('connected', () => {
  console.log('API has been connected to the endpoint');
});

api.on('disconnected', () => {
  console.log('API has been disconnected from the endpoint');
});

Parameters:

Returns: this

once

▸ once(type: ApiInterface$Events, handler: function): this

Inherited from ApiBase.once

Defined in Base.ts:211

description: Attach an one-time eventemitter handler to listen to a specific event

example:

api.once('connected', () => {
  console.log('API has been connected to the endpoint');
});

api.once('disconnected', () => {
  console.log('API has been disconnected from the endpoint');
});

Parameters:

Returns: this

<Static> create

▸ create(options?: ApiOptions | ProviderInterface): Promise<ApiPromise>

Defined in promise/index.ts:135

description: Creates an ApiPromise instance using the supplied provider. Returns an Promise containing the actual Api instance.

example:

import Api from '@polkadot/api/promise';

Api.create().then(async (api) => {
  const timestamp = await api.query.timestamp.now();

  console.log(`lastest block timestamp ${timestamp}`);
});

Parameters:

Returns: Promise<ApiPromise>