App API

Install

npm install --save @aragon/api

Import

ES6

import AragonApp, { providers } from '@aragon/api'

ES5 (CommonJS)

const AragonApp = require('@aragon/api').default
const providers = require('@aragon/api').providers

API Reference

AragonApp

This class is used to communicate with the wrapper in which the app is run.

Every method in this class sends an RPC message to the wrapper.

The app communicates with the wrapper using a messaging provider. The default provider uses the MessageChannel PostMessage API, but you may specify another provider to use (see the exported providers to learn more about them). You will most likely want to use the WindowMessage provider in your frontend.

Parameters

provider Object (optional, default MessagePortMessage): A provider used to send and receive messages to and from the wrapper. See providers.

Examples

import AragonApp, { providers } from '@aragon/api'

// The default provider should be used in background scripts
const backgroundScriptOfApp = new AragonApp()

// The WindowMessage provider should be used for front-ends
const frontendOfApp = new AragonApp(new providers.WindowMessage(window.parent))

Note Most of the returned observables will propagate errors from @aragon/wrapper (e.g. the Aragon client) if an RPC request failed. An example would be trying to use api.call('nonexistentFunction'). Multi-emission observables (e.g. api.accounts()) will forward the error without stopping the stream, leaving the subscriber to handle the error case.

Note Although many of the API methods return observables, many of them are single-emission observables that you can turn directly into a Promise. While this is seen as an "antipattern" by experienced RxJS users, it is highly convenient when you're not working fully in the context of streams and just need a particular async value (e.g. api.call('getVoteDetails', voteId)). The Aragon One team recommends this approach when first developing your apps if you are not already experienced with RxJS.

You can use the .toPromise() method on all single-emission observables safely (e.g. await api.call('getVoteDetails', voteId).toPromise()). If you receive a multi-emission observable (e.g. api.accounts()) but only care about its current value, you can use the first() operator, e.g. api.accounts().pipe(first()).toPromise().

Note All methods returning observables will only send their RPC requests upon the returned observable being subscribed. For example, calling api.increment() will NOT send an intent until you have subscribed to the returned observable. This is to ensure that responses cannot be accidentally skipped.

If you're not interested in the response, you can either make an "empty" subscription (i.e. api.increment().subscribe()), or turn it into a promise and await it (i.e. await api.increment().toPromise()).

Important Concepts / APIs

intents

To send an intent to the wrapper (i.e. invoke a method on your smart contract), simply call it on the instance of this class as if it was a JavaScript function.

For example, to execute the increment function in your app's smart contract:

const api = new AragonApp()

// Sends an intent to the wrapper that we wish to invoke `increment` on our app's smart contract
api
  .increment(1)
  .subscribe(
    txHash => console.log(`Success! Incremented in tx ${txHash}`),
    err => console.log(`Could not increment: ${err}`)
  )

The intent function returns a single-emission RxJS observable that emits the hash of the transaction that was sent or an error if the user choose not to sign the transaction.

You can also pass an optional object after all the required function arguments to specify some transaction options. They are the same values that can be passed to web3.eth.sendTransaction() and the full list can be seen in the web3.js documentation.

api.increment(1, { gas: 200000, gasPrice: 80000000 })

Some caveats to customizing transaction parameters:

from, to, data: will be ignored as aragonAPI will calculate those.
gas: If the intent cannot be performed directly (needs to be forwarded), the gas amount will be interpreted as the minimum amount of gas to send in the transaction. Because forwarding performs a heavier transaction gas-wise, if the gas estimation done by aragonAPI results in more gas than provided in the parameter, the estimated gas will prevail.

Pretransactions

Note Some intents may require additional transactions ahead of the actual intent, such as a token approval if the intent is to transfer tokens on the user's behalf. We use the concept of "pretransactions" to allow apps to easily declare that they require these actions.

Token Approvals

You can include a token parameter in the final options object if you need to grant the app an token allowance before a transaction. A slightly modified example from the Finance app:

intentParams = {
  token: { address: tokenAddress, value: amount }
  gas: 500000
}

api.deposit(tokenAddress, amount, reference, intentParams)

If you want to grant the token allowance to a different contract from the current app, you can pass along a spender paramater in the token object as follows:

intentParams = {
  token: { address: tokenAddress, value: amount, spender: otherContractAddress }
  gas: 500000
}

api.deposit(tokenAddress, amount, reference, intentParams)

store

Should be used as the main "event loop" in an application's background script (running inside a WebWorker). Listens for events, passes them through reducer, caches the resulting state, and re-emits that state for easy chaining.

The store has block caching automatically applied, such that subsequent loads of the application only fetch new events from a cached ("committed") block height (rather than from 0 or the app's initialization block).

The reducer takes the signature (state, event) à la Redux. Note that it must always return a state, even if it is unaltered by the event. Returning undefined will reset the reduced state to its initial null state.

Also note that the initial state is always null, not undefined, because of JSONRPC limitations.

Optionally takes a configuration object comprised of an init function, to re-initialize cached state, and an externals array for subscribing to external contract events. See below for more details.

Parameters

reducer Function: A function that reduces events to a state. The function is allowed to be async and can return a Promise that resolves to the new state.
options Object (optional, default {}): Optional configuration for the store:
- options.init Function (optional): An initialization function for the state that takes the cached state (null if no cached state exists) as a parameter and returns re-initialized state. The function is allowed to be async and can return a Promise that resolves to the state.
- options.externals Array (optional): An array of external contracts whose events the store will also be subscribed to. Each element in the array is an object containing:
  - contract Object: an external contract handle returned from api.external()
  - initializationBlock Number (optional, defaults to the application's own initialization block): block from which the external contract's events should be fetched from.

Returns Observable: A multi-emission observable that emits the application state every time it changes.

Lifecycle

A simple representation of the store's lifecycle:

Obtain the store's initial state by fetching any cached ("committed") state for the app, else use null as the initial state
Fetch past events from the contract and, starting with the initial state, reduce new state based on the incoming events

Note that there are some "custom" built-in events at this step:
- SYNC_STATUS_SYNCING: triggered when event fetching starts
- SYNC_STATUS_SYNCED: triggered when event fetching is complete

Cache the state at the end of this initial sync as the app's "committed" state to date
Subscribe to new events from the contract and reduce new state based on the incoming events. Note that this state is not cached as "commited" state and will not be available on the app's next start

Note that there are some "custom" built-in events at this step:
- ACCOUNT_TRIGGER: triggered whenever the currently connected account changes

If options.init and options.externals are given, the lifecycle becomes a bit more complicated:

Obtain the initial "committed" state, as before
If options.init is available, feed the initial state into options.init. Use the returned state from options.init as the new current state.
Fetch past events from the application contract and any given options.externals contracts, reducing new state from found events. Note that new events from both the application contract and external contracts are not fetched until all past events have been found.
Cache the state at the end of the initial sync as "committed" state, as before
Subscribe to new events from the contract and any given options.externals contracts, reducing new state based on the incoming events.

If the application emits its own triggers (see emitTrigger), the triggers will appear in the reducer only once the syncing phase for past events starts. Any triggers emitted before this will be ignored. Triggers are implicitly transformed into the web3 event schema of event (string) and returnValues (object).

Note The custom events are symbols and can be fetched from the events export of @aragon/api (e.g. import { events } from '@aragon/api'). All custom events conform to the web3 event schema of event (string) and returnValues (object).

Examples

A simple example:

// A simple reducer for a counter app

const state$ = api.store((state, event) => {
  // Initial state is always null
  if (state === null) state = 0

  switch (event.event) {
    case 'Increment':
      state++
      return state
    case 'Decrement':
      state--
      return state
  }

  // We must always return a state, even if unaltered
  return state
})

A more complicated example that also includes options.init and options.external

// A reducer that also reduces events from an external smart contract and uses
// an initialization function

const token = api.external(tokenAddress, tokenJsonInterface)

const initStore = async (cachedStoreState) => {
  // Perform any re-initializations on the cached committed state
  // This is useful for updating state (e.g. token balances, etc.) that may not
  // be // dependent on events
  const reinitializedStoreState = { ...cachedStoreState }

  // The state returned here will be used to start the reducer
  // (rather than the cached state)
  return reinitializedStoreState
}

const state$ = api.store(
  (state, event) => {
    // ...
  },
  {
    externals: {
      contract: token,
      initializationBlock: 0 // By default this uses the current AragonApp's initialization block
    },
    init: initStore,
  }
)

Available APIs

accounts

Get an array of the accounts the user currently controls over time.

Returns Observable: A multi-emission observable that emits an array of account addresses every time a change is detected.

network

Get the network the app is connected to over time.

Returns Observable: A multi-emission observable that emits an object with the connected network's id and type every time the network changes.

currentApp

Get information about this app (e.g. appAddress, appId, etc.).

Returns Observable: A single-emission observable that emits this app's details, including:

abi: this app's ABI
appAddress: this app's contract address
appId: this app's appId
appImplementationAddress: this app's implementation contract address, if any (only available if this app is a proxied AragonApp)
identifier: this app's self-declared identifier, if any
isForwarder: whether this app is a forwarder
kernelAddress: this app's attached kernel address (i.e. organization address)
name: this app's name, if available
roles (experimental): an array of this app's roles

Each app detail also includes an icon(size) function, that allows you to query for the app's icon (if available) based on a preferred size.

installedApps

Get the list of installed applications on the Kernel (organization) this app is attached to.

To get information about just the current app, use currentApp() instead.

Returns Observable: A multi-emission observable that emits an array of installed application objects every time a change to the installed applications is detected. Each object contains the same details as currentApp().

guiStyle

Can be ignored by non-GUI apps.

Get the current style of the client running this app.

Returns Observable: A multi-emission observable that emits an object containing two entries: appearance and theme.

appearance is currently one of light or dark. Other values could be passed in the future (e.g. black for OLED screens). It is always present and should be respected by apps to display a corresponding theme, unless theme is present.

theme contains an entire theme object (e.g. aragonUI's light theme) that should be applied to the app. It is optional and apps should respect it when present. If not possible, apps should respect the value of appearance.

path

Get the current path for the app over time. Useful with requestPath() to request and respond to in-app navigation changes.

Returns Observable: A multi-emission observable that emits a string for the app's current path every time the path changes.

requestPath

Request the current app be allowed to navigate to a different path. Different clients may behave differently, such as requesting user interaction, but all clients should only allow an app to change its path if it is currently visible to users.

Parameters

path string: The path to navigate to

Returns Observable: A single-emission observable that emits null on success or an error if the path request was rejected.

call

Perform a read-only call on the app's smart contract.

Parameters

method string: The name of the method to call
params ...any: An optional variadic number of parameters. The last parameter can be the call options (optional). See the web3.js doc for more details.

Returns Observable: A single-emission observable that emits the result of the call.

describeScript

Decodes an EVM callscript and tries to describe the transaction path that the script encodes.

Parameters

script string: The EVM callscript to describe

Returns Observable: A single-emission observable that emits the described transaction path. The emitted transaction path is an array of objects, where each item has a to, data, and description key.

describeTransaction

Tries to describe an Ethereum transaction based on its input data.

Parameters

transaction Object: Transaction object, holding to and data.

Returns Observable: A single-emission observable that emits the description, if describable. The result is an object with:

description: a string description
annotatedDescription: (if available) an array of objects annotating the description

events

Subscribe for events on your app's smart contract.

Parameters

options Object (optional): web3.eth.Contract.events()' options. Unless explicitly provided, fromBlock is always defaulted to the current app's initialization block.

Returns Observable: A multi-emission observable that emits Web3 events. Note that in the background, an eth_getLogs will first be done to retrieve events from the last unhandled block and only afterwards will an eth_subscribe be made to subscribe to new events.

pastEvents

Fetch events from past blocks on your app's smart contract.

Parameters

options Object (optional): web3.eth.Contract.getPastEvents()' options. Unless explicity provided, fromBlock is always defaulted to the current app's initialization block.

Returns Observable: An single-emission observable that emits an array of Web3 events from past blocks.

external

Creates a handle to interact with an external contract (i.e. a contract that is not your app's smart contract, such as a token).

Parameters

address string: The address of the external contract
jsonInterface Array<Object>: The JSON interface of the external contract

Examples

const token = api.external(tokenAddress, tokenJsonInterface)

// Retrieve the symbol of the token
token.symbol().subscribe(symbol => console.log(`The token symbol is ${symbol}`))

// Retrieve the token balance of an account
token
  .balanceOf(someAccountAddress)
  .subscribe(balance => console.log(`The balance of the account is ${balance}`))

Returns Object: An external smart contract handle, containing the following methods:

events(options): returns a multi-emission observable with individual events found, similar to events
pastEvents(options): returns a single-emission observable with an array of events found in past blocks, similar to pastEvents
Any other method on the handle will respond based on the given contract ABI:
- Calling any constant method (e.g. view, pure) will send a call to the smart contract and return a single emission observable with the result
- Calling any non-constant method will send an "external intent" to prompt a real transaction to the smart contract and return a single emission observable with the signature status (signed or not; similar to intents

requestSignMessage

Perform a signature using the personal_sign method.

Parameters

message string: The message to sign

Returns Observable: A single-emission observable that emits the signature hash on success or an error if the user chose not to sign the message.

Examples

  api
    .requestSignMessage('messageToSign')
    .subscribe(
      signature => {
        // use signature hash
      },
      err => {
        // handle error (including the user denying the signature request)
      }
    )

web3Eth

Request a white-listed web3.eth function call.

Currently the white-list includes:

estimateGas,
getAccounts,
getBalance,
getBlock,
getBlockNumber,
getBlockTransactionCount,
getCode,
getCoinbase,
getCompilers,
getGasPrice,
getHashrate,
getPastLogs,
getProtocolVersion,
getStorageAt,
getTransaction,
getTransactionCount,
getTransactionFromBlock,
getTransactionReceipt,
getWork,
getUncle,
isMining,
isSyncing

Parameters

params ...any: An optional variadic number of parameters for the function. See the web3.eth docs for more details.

Returns Observable: A single-emission observable with the result of the call.

Examples

api.web3Eth('getTransactionReceipt', trxHash).subscribe(
  receipt => {
    // use receipt
  },
  err => {
    // handle error
  }
)

const block = api.web3Eth('getBlock', blockNumber).toPromise()

const balance = await api.web3Eth('getBalance', connectedAccount).toPromise()

cache

Set a value in the application cache.

Parameters

key string: The cache key for the value
value any: The value to persist in the cache (must conform to the structured cloning algorithm)

Returns Observable: A single-emission observable that emits when the cache operation has been commited.

state

Observe the cached application state over time.

This method is also used to share state between the background script and front-end of your application.

Returns Observable: A multi-emission observable that emits the application state every time it changes. The type of the emitted values is application specific.

store

Reduce and cache application state based on events. See store documentation above.

triggers

Observe any emitted event triggers for this application.

Returns Observable: A multi-emission observable that emits on every emitted event trigger for this application (see emitTrigger()).

emitTrigger

Emit an event trigger to all running aragonAPI instances of your application, including the triggering instance. For example, if an application's frontend emits an event trigger, both the frontend and the background script's aragonAPI instances will receive it.

A common use case is to emit non-Ethereum event triggers from an application's frontend to its background script to recalculate reduced state based on a timer, user action, or external API request.

Parameters

name string: The name of the event
data Object (optional, default {}): event data

Returns void.

identify

Set the app identifier.

This identifier is used to distinguish multiple instances of your app, so choose something that provides additional context to the app instance.

Examples include: the name of a token that the app manages, the type of content that a TCR is curating, the name of a group etc.

Parameters

identifier string: The identifier of the app

Examples

api.identify('Customer counter')
// or
api.identify('Employee counter')

Returns void.

resolveAddressIdentity

Resolve an address' identity, using the highest priority provider.

Parameters

address string: Address to resolve

Returns Observable: A single-emission observable that emits the resolved identity or null if not found.

requestAddressIdentityModification

Request an address' identity be modified with the highest priority provider. The request will typically be handled by the Aragon client.

Parameters

address string: Address to modify

Returns Observable: A single-emission observable that emits if the modification succeeded or was cancelled by the user.

searchIdentities

Search for identities that match a given search term.

Parameters

searchTerm string: String to search for. Must be above a certain length, as defined by the handler (e.g. Aragon client uses minimum length of 3).

Returns Observable: A single-emission observable that emits with an array of any matching identities.

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