subspace-docs/getting-started.md

Getting Started

Installation

Subspace can be used in browser, node and native script environments. To get started install the package @status-im/subspace using npm or yarn by executing this command in your project directory:

# Using npm
npm install --save @status-im/subspace

# Using yarn
yarn add @status-im/subspace 

Importing the library

// ESM (might require babel / browserify)
import Subspace from '@status-im/subspace';  

// CommonJS
const Subspace = require('@status-im/subspace'); 

Connecting to a web3 provider

To interact with the EVM, Subspace requires a valid websockets Web3 provider.

const subspace = new Subspace(web3.currentProvider);
await subspace.init();

In addition to the provider, Subspace also accepts an options object with settings that can change its behavior:

• dbFilename - Name of the database where the information will be stored (default 'subspace.db')
• callInterval - Interval of time in milliseconds to query a contract/address to determine changes in state or balance (default: undefined. Obtains data every block).

Reacting to data

Once it's initialized, you can use Subspace's methods to track the contract state, events and balances. These functions return RxJS Observables which you can subscribe to, and obtain and transform the observed data via operators.

::: tip What is an Observable? The Observable type can be used to model push-based data sources such as DOM events, timer intervals, and sockets. In addition, observables are:

• Compositional: Observables can be composed with higher-order combinators.
• Lazy: Observables do not start emitting data until an observer has subscribed. :::

Further read

• RxJS Observables

Tracking state

You can track changes to a contract state variable, by specifying the view function and arguments to call and query the contract.

const stateObservable$ = Contract.methods.functionName().track();

::: tip Tracking the public variables of a contract State variables implicity create a view function when they're defined as public. The functionName would be the same as the variable name, and functionArgs would have a value when the type is a mapping or array (since these require an index value to query them). :::

Example:

const productTitle$ = ProductList.methods.products(0).track().map("title");
productTitle$.subscribe((title) => console.log("product title is " + title));

The subscriber will be triggered whenever the title changes

Tracking events

You can track events and react to their returned values.

const eventObservable$ = Contract.event.eventName().track();

Example:

const rating$ = Product.events.Rating().track().map("rating")).pipe(map(x => parseInt(x)));
rating$.subscribe((rating) => console.log("rating received: " + rating));

Event Sourcing

You can easily do event sourcing with subspace.

For e.g: if you needed to get the average rating of the last 5 events:

import { $average, $latest } from "@status-im/subspace";

const rating$ = Product.events.Rating().track().map("rating")).pipe(map(x => parseInt(x)));

rating$.pipe($latest(5), $average()).subscribe((rating) => {
  console.log("average rating of the last 5 events is " + rating)
});

Tracking balances

You can also track changes in both ETH and ERC20 token balances for each mined block or time interval depending on the callInterval configured.

Tracking ETH balance in an address:

const address = "0x0001020304050607080900010203040506070809";

subspace.trackBalance(address).subscribe((balance) => {
  console.log("ETH balance is ", balance)
});

Tracking ETH balance in a Contract:

Contract.trackBalance().subscribe((balance) => {
  console.log("ETH balance is ", balance)
});

Tracking an ERC20 balance in a Contract:

const tokenAddress = "0x744d70fdbe2ba4cf95131626614a1763df805b9e"; // SNT Address

const myBalanceObservable$ = Contract.trackBalance(tokenAddress);

::: warning Balances are returned as a string containing the value in wei. :::

Subscriptions

Once you have an Observable, you may receive a stream of data by creating a subscription.Subscriptions are triggered each time an observable emits a new value. These subscription receive a callback that must have a parameter which represents the value received from the observable (a contract state variable, an event, or the balance of an address); and they return an object representing the subscription.

Subscriptions can be disposed by executing the method unsubscribe() liberating the resource held by it:

const myBalanceObservable$ = subspace.trackBalance(address, tokenAddress);
const subscription = myBalanceObservable$.subscribe(value => { 
  console.log("The balance is: ", value); 
});

// ...

subscription.unsubscribe();

Further read

• RxJS Subscriptions

Cleanup

If Subspace is not needed anymore, you need can invoke close() to dispose and perform the cleanup necessary to remove the internal subscriptions and interval timers created by Subspace during its normal execution, thus avoiding any potential memory leak.

subspace.close();

::: warning What about subscriptions created with our observables? Any subscription created via the tracking methods must be unsubscribed manually (in the current version). :::