---
eip: 1193
title: Ethereum Provider JavaScript API
author: Ryan Ghods (@ryanio), Marc Garreau (@marcgarreau)
discussions-to: https://ethereum-magicians.org/t/eip-1193-ethereum-provider-javascript-api/640
status: Draft
type: Standards Track
category: Interface
created: 2018-06-30
requires: 1102
---

## Summary

This EIP formalizes an Ethereum Provider JavaScript API for consistency across clients and applications.

The provider is designed to be minimal, containing 3 methods: `send`, `subscribe`, and `unsubscribe`. It emits 4 types of events: `connect`, `close`, `networkChanged`, and `accountsChanged`.

## API

### Send

```js
ethereum.send(method: String, params?: Array<any>): Promise<any>;
```

Promise resolves with `result` or rejects with `Error`.

See the [available methods](https://github.com/ethereum/wiki/wiki/JSON-RPC#json-rpc-methods).

### Subscriptions

#### Subscribe

```js
ethereum.subscribe(subscriptionType: String, params?: Array<any>): Promise<String|Error>;
```

Promise resolves with `subscriptionId: String` or rejects with `Error`.

See the [types of subscriptions](https://github.com/ethereum/go-ethereum/wiki/RPC-PUB-SUB#supported-subscriptions).

Results emit on `subscriptionId` using [EventEmitter](https://nodejs.org/api/events.html). Attach listeners with:

```js
ethereum.on(subscriptionId, listener: (result: any) => void): this;
```

The event emits with `result`, the subscription `result` or an `Error` object.

#### Unsubscribe

```js
ethereum.unsubscribe(subscriptionId: String): Promise<Boolean|Error>;
```

Promise resolves with `success: Boolean` or rejects with `Error`.

All [EventEmitter](https://nodejs.org/api/events.html) listeners on `subscriptionId` will also be removed.

### Events

Events are emitted using [EventEmitter](https://nodejs.org/api/events.html).

#### connect

The provider emits `connect` on connect to a network.

```js
ethereum.on('connect', listener: () => void): this;
```

You can detect which network by sending `net_version`:

```js
const network = await ethereum.send('net_version');
> '1'
```

#### close

The provider emits `close` on disconnect from a network.

```js
ethereum.on('close', listener: (code: Number, reason: String) => void): this;
```

The event emits with `code` and `reason`. The code follows the table of [`CloseEvent` status codes](https://developer.mozilla.org/en-US/docs/Web/API/CloseEvent#Status_codes).

#### networkChanged

The provider emits `networkChanged` on connect to a new network.

```js
ethereum.on('networkChanged', listener: (networkId: String) => void): this;
```

The event emits with `networkId`, the new network returned from `net_version`.

#### accountsChanged

The provider emits `accountsChanged` if the accounts returned from the provider (`eth_accounts`) changes.

```js
ethereum.on('accountsChanged', listener: (accounts: Array<String>) => void): this;
```

The event emits with `accounts`, an array of the accounts' public keys.

### Constructor

```js
ethereum.constructor.name;
> 'EthereumProvider'
```

## Examples

```js
// Request Ethereum Provider (EIP 1102)
window.addEventListener('message', event => {
  if (event.data && event.data.type === 'ETHEREUM_PROVIDER_SUCCESS') {
    start(window.ethereum);
  }
});
window.postMessage({ type: 'ETHEREUM_PROVIDER_REQUEST' }, this.origin);

function start(ethereum) {
  // A) Primary use case - set provider in web3.js
  web3.setProvider(ethereum);

  // B) Secondary use case - use provider object directly
  // Example: Log accounts
  ethereum
    .send('eth_accounts')
    .then(accounts => {
      console.log(`Accounts:\n${accounts.join('\n')}`);
    })
    .catch(error => {
      console.error(
        `Error fetching accounts: ${error.message}.
         Code: ${error.code}. Data: ${error.data}`
      );
    });

  // Example: Log last block
  ethereum
    .send('eth_getBlockByNumber', ['latest', 'true'])
    .then(block => {
      console.log(`Block ${block.number}:\n${block}`);
    })
    .catch(error => {
      console.error(
        `Error fetching last block: ${error.message}.
         Code: ${error.code}. Data: ${error.data}`
      );
    });

  // Example: Log new blocks
  let subId;
  ethereum
    .subscribe('newHeads')
    .then(subscriptionId => {
      subId = subscriptionId;
      ethereum.on(subscriptionId, block => {
        if (result instanceOf Error) {
          const error = result;
          console.error(
            `Error from newHeads subscription: ${error.message}.
             Code: ${error.code}. Data: ${error.data}`
          );
        } else {
          console.log(`New block ${block.number}:\n${block}`);
        }
      });
    })
    .catch(error => {
      console.error(
        `Error making newHeads subscription: ${error.message}.
         Code: ${error.code}. Data: ${error.data}`
       );
    });
  // to unsubscribe
  ethereum
    .unsubscribe(subId)
    .then(result => {
      console.log(`Unsubscribed newHeads subscription ${subscriptionId}`);
    })
    .catch(error => {
      console.error(
        `Error unsubscribing newHeads subscription: ${error.message}.
         Code: ${error.code}. Data: ${error.data}`
      );
    });

  // Example: Log when accounts change
  const logAccounts = accounts => {
    console.log(`Accounts:\n${accounts.join('\n')}`);
  };
  ethereum.on('accountsChanged', logAccounts);
  // to unsubscribe
  ethereum.removeListener('accountsChanged', logAccounts);

  // Example: Log if connection ends
  ethereum.on('close', (code, reason) => {
    console.log(
      `Ethereum provider connection closed: ${reason}. Code: ${code}`
    );
  });
}
```

## Specification

### Send

The `send` method **MUST** send a properly formatted [JSON-RPC request](https://www.jsonrpc.org/specification#request_object).

If the Ethereum JSON-RPC API returns a response object with no error, then the Promise **MUST** resolve with the `response.result` object untouched by the implementing Ethereum Provider.

If the Ethereum JSON-RPC API returns response object that contains an error property then the Promise **MUST** be rejected with an Error object containing the `response.error.message` as the Error message, `response.error.code` as a code property on the error and `response.error.data` as a data property on the error.

If an error occurs during processing, such as an HTTP error or internal parsing error, then the Promise **MUST** be rejected with an Error object.

If the implementing Ethereum Provider is not talking to an external Ethereum JSON-RPC API provider then it **MUST** resolve with an object that matches the JSON-RPC API object as specified in the [Ethereum JSON-RPC documentation](https://github.com/ethereum/wiki/wiki/JSON-RPC).

### Subscriptions

The `subscribe` method **MUST** send a properly formatted [JSON-RPC request](https://www.jsonrpc.org/specification#request_object) with method `eth_subscribe` and params `[subscriptionType: String, {...params: Array<any>}]` and **MUST** return a Promise that resolves with `subscriptionId: String` or rejected with an Error object.

The `unsubscribe` method **MUST** send a properly formatted [JSON-RPC request](https://www.jsonrpc.org/specification#request_object) with method `eth_unsubscribe` and params `[subscriptionId: String]` and **MUST** return a Promise that resolves with `result: Boolean` or rejected with an Error object.

If the `unsubscribe` method returns successfully with a `True` result, the implementing provider **MUST** remove all listeners on the `subscriptionId` using `ethereum.removeAllListeners(subscriptionId);`.

If an error occurs during processing of the subscription, such as an HTTP error or internal parsing error then the Promise **MUST** return with an Error object.

The implementing Ethereum Provider **MUST** emit every subscription response `result` with the eventName `subscriptionId`.

If an error occurs or the network changes during the listening of the subscription, the Ethereum Provider **MUST** emit an Error object to the eventName `subscriptionId`.

If the implementing provider does not support subscriptions, then it **MUST** leave the `subscribe` and `unsubscribe` methods undefined.

### Events

If the network connects, the Ethereum Provider **MUST** emit an event named `connect`.

If the network connection closes, the Ethereum Provider **MUST** emit an event named `close` with args `code: Number, reason: String` following the [status codes for `CloseEvent`](https://developer.mozilla.org/en-US/docs/Web/API/CloseEvent#Status_codes).

If the network the provider is connected to changes, the provider **MUST** emit an event named `networkChanged` with args `networkId: String` containing the ID of the new network (using the Ethereum JSON-RPC call `net_version`).

If the accounts connected to the Ethereum Provider change, the Ethereum Provider **MUST** send an event with the name `accountsChanged` with args `accounts: Array<String>` containing the accounts' public key(s).

### Class

The name of the constructor of the Ethereum Provider **MUST** be `EthereumProvider`.

### web3.js Provider

The implementing Ethereum Provider **MUST** be compatible as a `web3.js` provider. This is accomplished by providing two methods in the `EthereumProvider`: `sendAsync(payload: Object, callback: (error: any, result: any) => void): void` and `isConnected(): Boolean`.

### Error object and codes

If an Error object is returned, it **MUST** contain a human readable string message describing the error and **SHOULD** populate the `code` and `data` properties on the error object with additional error details.

Appropriate error codes **SHOULD** follow the table of [`CloseEvent` status codes](https://developer.mozilla.org/en-US/docs/Web/API/CloseEvent#Status_codes).

## Sample Class Implementation

```js
class EthereumProvider extends EventEmitter {
  constructor() {
    // Call super for `this` to be defined
    super();

    // Init storage
    this._isConnected = false;
    this._nextJsonrpcId = 0;
    this._promises = {};
    this._activeSubscriptions = [];

    // Fire the connect
    this._connect();

    // Listen for jsonrpc responses
    window.addEventListener('message', this._handleJsonrpcMessage.bind(this));
  }

  /* Methods */

  send(method, params = []) {
    if (!method || typeof method !== 'string') {
      return new Error('Method is not a valid string.');
    }

    if (!(params instanceof Array)) {
      return new Error('Params is not a valid array.');
    }

    const id = this._nextJsonrpcId++;
    const jsonrpc = '2.0';
    const payload = { jsonrpc, id, method, params };

    const promise = new Promise((resolve, reject) => {
      this._promises[payload.id] = { resolve, reject };
    });

    // Send jsonrpc request to Mist
    window.postMessage(
      { type: 'mistAPI_ethereum_provider_write', message: payload },
      origin
    );

    return promise;
  }

  subscribe(subscriptionType, params) {
    return this.send('eth_subscribe', [subscriptionType, ...params]).then(
      subscriptionId => {
        this._activeSubscriptions.push(subscriptionId);
      }
    );
  }

  unsubscribe(subscriptionId) {
    return this.send('eth_unsubscribe', [subscriptionId]).then(success => {
      if (success) {
        // Remove subscription
        this._activeSubscription = this._activeSubscription.filter(
          id => id !== subscriptionId
        );
        // Remove listeners on subscriptionId
        this.removeAllListeners(subscriptionId);
      }
    });
  }

  /* Internal methods */

  _handleJsonrpcMessage(event) {
    // Return if no data to parse
    if (!event || !event.data) {
      return;
    }

    let data;
    try {
      data = JSON.parse(event.data);
    } catch (error) {
      // Return if we can't parse a valid object
      return;
    }

    // Return if not a jsonrpc response
    if (!data || !data.message || !data.message.jsonrpc) {
      return;
    }

    const message = data.message;
    const { id, method, error, result } = message;

    if (typeof id !== 'undefined') {
      const promise = this._promises[id];
      if (promise) {
        // Handle pending promise
        if (data.type === 'error') {
          promise.reject(message);
        } else if (message.error) {
          promise.reject(error);
        } else {
          promise.resolve(result);
        }
        delete this._promises[id];
      }
    } else {
      if (method && method.indexOf('_subscription') > -1) {
        // Emit subscription result
        const { subscription, result } = message.params;
        this.emit(subscription, result);
      }
    }
  }

  /* Connection handling */

  _connect() {
    // Send to Mist
    window.postMessage({ type: 'mistAPI_ethereum_provider_connect' }, origin);

    // Reconnect on close
    this.once('close', this._connect.bind(this));
  }

  /* Events */

  _emitConnect() {
    this._isConnected = true;
    this.emit('connect');
  }

  _emitClose(code, reason) {
    this._isConnected = false;
    this.emit('close', code, reason);

    // Send Error objects to any open subscriptions
    this._activeSubscriptions.forEach(id => {
      const error = new Error(
        `Provider connection to network closed.
         Subscription lost, please subscribe again.`
      );
      this.emit(id, error);
    });
    // Clear subscriptions
    this._activeSubscriptions = [];
  }

  _emitNetworkChanged(networkId) {
    this.emit('networkChanged', networkId);
  }

  _emitAccountsChanged(accounts) {
    this.emit('accountsChanged', accounts);
  }

  /* web3.js provider compatibility */

  sendAsync(payload, callback) {
    return this.send(payload.method, payload.params)
      .then(result => {
        const response = payload;
        response.result = result;
        callback(null, response);
      })
      .catch(error => {
        callback(error, null);
        // eslint-disable-next-line no-console
        console.error(
          `Error from EthereumProvider sendAsync ${payload}: ${error}`
        );
      });
  }

  isConnected() {
    return this._isConnected;
  }
}
```

## Copyright

Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).