Decentralized Apps

Building a decentralized app doesn’t have to be hard, use these tools from NEO•ONE to make it quick and easy.

In addition to the client APIs we’ve already walked through, there are a few properties on the Client that help make your app reactive. We’ll also cover using the NEO•ONE Developer Tools to help speed up manual testing of your dapp.


NEO•ONE uses Observables with RxJS to enable reactivity in dapps. The Client class has several Observable properties that can be subscribed to in order to update application state and the application UI. The most commonly used is the block$ property:

class Client {
   * Emits a value whenever a block is persisted to the blockchain.
   * Immediately emits the latest block/network when subscribed to.
  public readonly block$: Observable<{
    readonly block: Block;
    readonly network: NetworkType;

The Observable emits a value whenever a new block is persisted to the blockchain for the given network. The network property corresponds to the currently selected user account’s network. The Observable automatically updates to start emitting new blocks from another network whenever the underlying network changes due to a change in the selected user account.

We can update application state that depends on new blocks by subscribing to the block$ Observable:

client.block$.subscribe(({ block, network }) => {
  // Update application state using the latest block and network


If you’re using React, check out the FromStream component in the React advanced guide for a streamlined way to integrate Observables in your application. If you’re using Angular or Vue, check out the Angular or Vue advanced guides for examples with those frameworks.

One common use-case is to update the user balance whenever a new block is persisted. For example, if we’re displaying the user’s NEO and GAS balance:

    switchMap(async () => {
      const userAccount = client.getCurrentUserAccount();
      if (userAccount === undefined) {
        return undefined;

      const account = await client.getAccount(;

      return { neo: account.balances[Hash256.NEO], gas: account.balances[Hash256.GAS] };
  .subscribe((result) => {
    if (result === undefined) {
      // Update the UI when a user account is not selected
    } else {
      const { neo, gas } = result;
      // Update the UI with the new neo and gas values.

This is a fairly common pattern, so Client already exposes an Observable for it:

class Client {
   * Emits a value whenever a new user account is selected and whenever a block is persisted to the blockchain.
   * Immediately emits the latest value when subscribed to.
  public readonly accountState$: Observable<
    | {
        readonly currentUserAccount: UserAccount;
        readonly account: Account;
    | undefined

Thus, we can simplify the above example to just:

client.accountState$.subscribe((result) => {
  if (result === undefined) {
    // Update the UI when a user account is not selected
  } else {
    const neo = result.account.balances[Hash256.NEO];
    const gas = result.account.balances[Hash256.GAS];
    // Update the UI with the new neo and gas values.

Take a look at the @neo-one/client reference for details on all available Observables.

Developer Tools

Developer Tools have not been thoroughly tested for N3 yet and may not work at this point in time.

NEO•ONE Developer Tools simplify the process of developing and manually testing your dapp. They contain all of the functionality necessary to control your private network:

  • Immediately run consensus
  • Fast forward to a future time
  • Reset the local network to it’s initial state
  • Full wallet implementation with the same set of pre-configured wallets as tests
  • Settings for controlling automatic consensus and system fees, seconds per block and adding NEP-5 token addresses to the wallet
  • Notifications when transactions are confirmed with links to view the transaction on a local NEO Tracker instance

Enabling the Developer Tools is easy:

const client = createClient();
const developerClients = createDeveloperClients();
DeveloperTools.enable({ client, developerClients });

Simply use the generated helper functions in src/neo-one/client.ts to construct the various clients the Developer Tools require and then call enable.


If you’ve integrated NEO•ONE using the React advanced guide, then the Developer Tools are automatically enabled with no additional calls or configuration required.

When building for production, the Developer Tools are automatically replaced with an empty implementation, so they won’t show up for your users nor affect the bundle size.

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