Client APIs

Now it’s time to take a look at the client APIs and learn how to interact with smart contracts from a dapp.

The NEO•ONE client APIs are organized into two packages, @neo-one/client which contains the most commonly used functionality, and @neo-one/client-full which contains extended but rarely used functionality. In general a dapp developer only needs to concern themselves with the APIs offered by @neo-one/client. Learn more about the @neo-one/client-full APIs in the Extended Client APIs advanced guide.


The @neo-one/client APIs center around instances of the Client class. The Client class abstracts away user accounts and even how those accounts are provided to your dapp, for example, they might come from an extension like NEX, dapp browser like nOS or through some other integration.


Do not roll your own wallet when creating a dapp. This fractures the ecosystem and in the worst case, requires users to trust every dapp with their private keys. Instead, configure your Client to work with one of the existing wallets. Read more in the User Accounts advanced guide.

The Client class also contains a few methods that may be useful in the course of developing a dapp:

  • getCurrentUserAccount(): UserAccount | undefined - Returns the currently selected UserAccount. Returns undefined if there are no UserAccounts.
  • getCurrentNetwork(): NetworkType - Returns the currently selected network, a string that will be 'main' for the MainNet, 'test' for the TestNet, and typically 'local' for a local private network.
  • getAccount(id: UserAccountID): Promise<Account> - Returns an object containing the native asset balances for a given UserAccountID.

The Client class also contains two methods for creating transactions.

class Client {
  public async transfer(
    amount: BigNumber,
    asset: Hash256String,
    to: AddressString,
    options?: TransactionOptions,
  ): Promise<TransactionResult<TransactionReceipt, InvocationTransaction>>;
  public async transfer(transfers: ReadonlyArray<Transfer>, options?: TransactionOptions): Promise<TransactionResult>;

  public async claim(optionsIn?: TransactionOptions): Promise<TransactionResult>;
  • transfer creates a transaction for transferring native assets from the currently selected account (by default) to the specified address(es).
  • claim creates a transaction for claiming unclaimed GAS for the currently selected account.

We’ll go into more detail on the shape of the TransactionResult object and the semantics of creating transactions in the next chapter.

All methods that relay transactions to the blockchain optionally accept a TransactionOptions object (or an extension of it) for customizing the relayed transaction:

interface TransactionOptions {
   * The `UserAccount` that the transaction is "from", i.e. the one that will be used for native asset transfers, claims, and signing the transaction.
   * If unspecified, the currently selected `UserAccount` is used as the `from` address.
   * DApp developers will typically want to leave this unspecified.
  from?: UserAccountID;
   * Additional attributes to include with the transaction.
  attributes?: ReadonlyArray<Attribute>;
   * An optional network fee to include with the transaction.
  networkFee?: BigNumber;
   * A maximum system fee to include with the transaction. Note that this is a maximum, the client APIs will automatically calculate and add a system fee to the transaction up to the value specified here.
   * Leaving `systemFee` `undefined` is equivalent to `new BigNumber(0)`, i.e. no system fee.
   * A `systemFee` of `-1`, i.e. `new BigNumber(-1)` indicates no limit on the fee. This is typically used only during development.
  systemFee?: BigNumber;
  monitor?: Monitor;


You’ll notice that all methods in the client APIs take a Monitor object. This object encapsulates logging throughout NEO•ONE. Find out more in the Monitor advanced guide.

Putting this all together, if we wanted to transfer funds to another account, but only if the account is empty, we would do:

const account = await client.getAccount(otherAccountID);
if (account.balances[Hash256.NEO] === undefined) {
  await client.transfer.confirmed(new BigNumber(10), Hash256.NEO, otherAccountID.address);

We’ll learn more about the confirmed property in the next chapter. Also take note of the Hash256.NEO property, which works just like the Hash256.NEO property in smart contracts and can be imported directly from @neo-one/client.

Toolchain Code Generation

The NEO•ONE toolchain generates many files that contain helpers and APIs that are essential for dapp development. Running neo-one build will emit TypeScript files. Let’s briefly cover what each one contains.


The output directory for generated files is configurable. You can also change the configuration to emit pure JavaScript files instead of TypeScript. See the Configuration reference for details.

For each contract, the toolchain will emit 3 files:

  • one/generated/<ContractName>/abi.ts - Contains the ABI that generates the client smart contract APIs at runtime that we’ll discuss in the next chapter.
  • one/generated/<ContractName>/contract.ts - Contains the smart contract definition, which contains the ABI, the source maps for the contract and a mapping from network name to deployed address for the smart contract. Initially the network mapping will only contain the local network which represents your local development network. Once you deploy your smart contract to the TestNet or MainNet, it will also contain deployed contract addresses for those networks. The client APIs automatically choose which address to work with based on the network of the user account that is initiating the request. This file also contains a helper function for creating the smart contract APIs given a Client.
  • one/generated/<ContractName>/types.ts - Contains the TypeScript type definitions for the smart contract client APIs.

6 files will also be emitted that are common to all of your smart contracts:

  • one/generated/client.ts - Contains helper functions for creating a fully configured Client. The Client is also configured automatically for local development with 11 user accounts that each have varying amounts of NEO and GAS. Additionally contains helper functions for creating DeveloperClients and LocalClients which can be used to control your local development environment. These are generally passed on to the NEO•ONE Developer Tools which we’ll talk about in a later chapter.
  • one/generated/projectID.ts - This contains a unique identifier for your project. The NEO•ONE toolchain stores some of the information it needs locally on your machine referenced by this project identifier. This information should not be checked in, however we need to be able to associate it with a given project, hence we have the projectID.
  • one/generated/react.tsx - Contains two react components, that when used together allow you to easily access all of the tools you need to write a dapp with React throughout your component tree. Read more in the React advanced guide.
  • one/generated/sourceMaps.ts - Contains all of the smart contract source maps. These source maps are not included in the production build in order to reduce the bundle size.
  • one/generated/test.ts - Contains the withContracts test helper. We’ll learn more about this helper in the following chapters.
  • one/generated/types.ts - Contains the Contracts type whose properties are the smart contract APIs for your dapp.


Integrating the NEO•ONE client APIs in a vanilla JavaScript or TypeScript application is very simple - assuming we have a contract called Token and we’re in the src/index.ts file using the default NEO•ONE toolchain paths:

import { createClient, createTokenSmartContract } from '../one/generated';

const client = createClient();
const token = createTokenSmartContract(client);

Now we can use both the base blockchain APIs offered by the Client class and the generated smart contract APIs that correspond to the Token contract.


As you prepare your dapp for production, you’ll likely want to configure additional UserAccountProviders in the Client. Learn more about UserAccounts and UserAccountProviders in the User Accounts advanced guide.


@neo-one/client exports many utility functions for working with private keys, addresses, public keys and script hashes:

  • The most common come in the form of conversion functions: <fromFormat>To<toFormat>, for example, privateKeyToAddress. See the full list in the @neo-one/client reference.
  • createPrivateKey returns a new private key.
  • decryptNEP2, encryptNEP2 and isNEP2 implement NEP-2
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