Agent

@dfinity/agent

JavaScript and TypeScript library to interact with the Internet Computer for Node.js and browser applications.

Do you want to know more about developing on the Internet Computer? Visit the Developer Docs.

Additional API Documentation can be found here.

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Installation

Using agent:

npm i --save @dfinity/agent

In the browser:

import * as agent from '@dfinity/agent';

or using individual exports:

import { Actor, HttpAgent } from '@dfinity/agent';

In Node.js

const DfinityAgent = require('@dfinity/agent');

or using individual exports:

const { Actor, HttpAgent } = require('@dfinity/agent');

Using an Agent

The agent is a low-level interface that the Actor uses to encode and decode messages to the Internet Computer. It provides call, query and readState methods to the Actor, as well as a few additional utilities. For the most part, calls through the agent are intended to be structured through an Actor, configured with a canister interface that can be automatically generated from a Candid interface.

Initializing an Actor

The most common use for the agent is to create an actor. This is done by calling the Actor.createActor constructor:

Actor.createActor(interfaceFactory: InterfaceFactory, configuration: ActorConfig): ActorSubclass<T>

The interfaceFactory is a function that returns a runtime interface that the Actor uses to strucure calls to a canister. The interfaceFactory can be written manually, but it is recommended to use the dfx generate command to generate the interface for your project, or to use the didc tool to generate the interface for your project.

Actors can also be initialized to include the boundary node http headers, This is done by calling the Actor.createActor constructor:

Actor.createActorWithHttpDetails(interfaceFactory: InterfaceFactory, configuration: ActorConfig): ActorSubclass<ActorMethodMappedWithHttpDetails<T>>

Inspecting an actor’s agent

Use the Actor.agentOf method to get the agent of an actor:

const defaultAgent = Actor.agentOf(defaultActor);

This is useful if you need to replace or invalidate the identity used by an actor’s agent.

For example, if you want to replace the identity of an actor’s agent with a newly authenticated identity from Internet Identity, you can do so by calling the Actor.replaceAgent method:

defaultAgent.replaceIdentity(await authClient.getIdentity());

Tips for using fetch

The agent uses the browser fetch API to make calls to the Internet Computer. If you are not using the agent in the browser, you can pass a custom fetch implementation to the agent’s constructor. This is useful if you want to use a custom fetch implementation, such as one that adds authentication headers to the request. We recommend using the isomorphic-fetch package to provide a consistent fetch API across Node.js and the browser. You will also need to provide a host option to the agent’s constructor, as the agent will not be able to determine the host from the global context.

For example,

import fetch from 'isomorphic-fetch';
import { HttpAgent } from '@dfinity/agent';

const host = process.env.DFX_NETWORK === 'local' ? 'http://127.0.0.1:4943' : 'https://icp-api.io';

const agent = new HttpAgent({ fetch, host });

You can also pass fetchOptions to the agent’s constructor, which will be passed to the fetch implementation. This is useful if you want to pass additional options to the fetch implementation, such as a custom header.

For example,

import fetch from 'isomorphic-fetch';
import { HttpAgent } from '@dfinity/agent';

const host = process.env.DFX_NETWORK === 'local' ? 'http://127.0.0.1:4943' : 'https://ic0.app';

/**
 * @type {RequestInit}
 */
const fetchOptions = {
  headers: {
    'X-Custom-Header': 'value',
  },
};

const agent = new HttpAgent({ fetch, host, fetchOptions });