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NEAR JavaScript SDK

Quick Start

Use create-near-app to quickly get started writing smart contracts in JavaScript on NEAR.

npx create-near-app

This will scaffold a basic template for you 😎

Learn more in our Quick Start guide.

Running Examples

There are a couple of contract examples in the project:

To build all examples, run yarn build in examples/. To test all examples, run yarn test. You can also build and test one specific example with yarn build:<example-name> and yarn test:<example-name>, see examples/package.json.

To deploy and call a contract on a NEAR node, use near-cli's near deploy and near call.

Test

We recommend to use near-workspaces to write tests for your smart contracts. See any of the examples for how tests are setup and written.

Error Handling in NEAR-SDK-JS

If you want to indicate an error happened and fail the transaction, just throw an error object in JavaScript. The compiled JavaScript contract includes error handling capability. It will catch throwed errors and automatically invoke panic_utf8 with "{error.message}\n:{error.stack}". As a result, transaction will fail with "Smart contract panicked: {error.message}\n{error.stack}" error message. You can also use an error utilities library to organize your errors, such as verror.

When your JS code or library throws an error, uncaught, the transaction will also fail with GuestPanic error, with the error message and stacktrace.

When call host function with inappropriate type, means incorrect number of arguments or arg is not expected type:

if arguments less than params, remaining argument are set as 'undefined'
if arguments more than params, remaining argument are ignored
if argument is different than the required type, it'll be coerced to required type
if argument is different than the required type but cannot be coerced, will throw runtime type error, also with message and stacktrace

NEAR-SDK-JS API Reference

All NEAR blockchain provided functionality (host functions) are defined in src/api.ts and exported as near. You can use them by:

import { near } from "near-sdk-js";

// near.<api doucmented below>. e.g.:
let signer = near.signerAccountId();

To use nightly host functions, such as altBn128G1Sum, your contract need to be built with nightly enabled. Use:

export NEAR_NIGHTLY=1
yarn build

About Type

NEAR-SDK-JS is written in TypeScript, so every API function has a type specified by signature that looks familiar to JavaScript/TypeScript Developers. Two types in the signature need a special attention:

Most of the API take bigint instead of Number as type. This because JavaScript Number cannot hold 64 bit and 128 bit integer without losing precision.
Bytes in both arguments and return represent a byte buffer, internally it's a JavaScript String Object. Any binary data 0x00-0xff is stored as the char '\x00-\xff'. This is because QuickJS doesn't have Uint8Array in C API.
- To ensure correctness, every Bytes argument need to be pass in with the bytes() function to runtime type check it's indeed a Bytes.
- If Bytes is too long that bytes() can cause gas limit problem, such as in factory contract, represents the content of contract to be deployed. In this case you can precheck and guarantee the correctness of the content and use without bytes().

Context API

function currentAccountId(): string;
function signerAccountId(): string;
function signerAccountPk(): Bytes;
function predecessorAccountId(): string;
function input(): Bytes;
function blockIndex(): bigint;
function blockHeight(): bigint;
function blockTimestamp(): bigint;
function epochHeight(): bigint;
function storageUsage(): bigint

Economics API

function accountBalance(): bigint;
function accountLockedBalance(): bigint;
function attachedDeposit(): bigint;
function prepaidGas(): bigint;
function usedGas(): bigint;

Math API

function randomSeed(): Bytes;
function sha256(value: Bytes): Bytes;
function keccak256(value: Bytes): Bytes;
function keccak512(value: Bytes): Bytes;
function ripemd160(value: Bytes): Bytes;
function ecrecover(hash: Bytes, sign: Bytes, v: bigint, malleability_flag: bigint): Bytes | null;

Miscellaneous API

function valueReturn(value: Bytes);
function panic(msg?: string);
function panicUtf8(msg: Bytes);
function log(msg: string);
function logUtf8(msg: Bytes);
function logUtf16(msg: Bytes);

Promises API

function promiseCreate(account_id: string, method_name: string, arguments: Bytes, amount: bigint, gas: bigint): bigint;
function promiseThen(promise_index: bigint, account_id: string, method_name: string, arguments: Bytes, amount: bigint, gas: bigint): bigint;
function promiseAnd(...promise_idx: bigint): bigint;
function promiseBatchCreate(account_id: string): bigint;
function promiseBatchThen(promise_index: bigint, account_id: string): bigint;

Promise API actions

function promiseBatchActionCreateAccount(promise_index: bigint);
function promiseBatchActionDeployContract(promise_index: bigint, code: Bytes);
function promiseBatchActionFunctionCall(promise_index: bigint, method_name: string, arguments: Bytes, amount: bigint, gas: bigint);
function promiseBatchActionFunctionCallWeight(promise_index: bigint, method_name: string, arguments: Bytes, amount: bigint, gas: bigint, weight: bigint);

function promiseBatchActionTransfer(promise_index: bigint, amount: bigint);
function promiseBatchActionStake(promise_index: bigint, amount: bigint, public_key: Bytes);
function promiseBatchActionAddKeyWithFullAccess(promise_index: bigint, public_key: Bytes, nonce: bigint);
function promiseBatchActionAddKeyWithFunctionCall(promise_index: bigint, public_key: Bytes, nonce: bigint, allowance: bigint, receiver_id: string, method_names: string);
function promiseBatchActionDeleteKey(promise_index: bigint, public_key: Bytes);
function promiseBatchActionDeleteAccount(promise_index: bigint, beneficiary_id: string);

Promise API results

function promiseResultsCount(): bigint;
function promiseResult(result_idx: bigint, register_id: bigint): bigint;
function promiseReturn(promise_idx: bigint);

Storage API

function storageWrite(key: Bytes, value: Bytes, register_id: bigint): bigint;
function storageRead(key: Bytes, register_id: bigint): bigint;
function storageRemove(key: Bytes, register_id: bigint): bigint;
function storageHasKey(key: Bytes): bigint;

Validator API

function validatorStake(account_id: string): bigint;
function validatorTotalStake(): bigint;

Alt BN128

function altBn128G1Multiexp(value: Bytes, register_id: bigint);
function altBn128G1Sum(value: Bytes, register_id: bigint);
function altBn128PairingCheck(value: Bytes): bigint;

NearBindgen and other decorators

You can write a simple smart contract by only using low-level APIs, such as near.input(), near.storageRead(), etc. In this case, the API of your contract will consist of all the exported JS functions. You can find an example of such a contract here.

But if you want to build a more complex contracts with ease, you can use decorators from this SDK that will handle serialization, deserialization, and other boilerplate operations for you.

In order to do that, your contract must be a class decorated with @NearBindgen({}). Each method in this class with @call({}), @view({}), and @initialize({}) decorators will become functions of your smart contract. call functions can change state, and view functions can only read it.

Your class must have a constructor(). You will not be able to call it, which is why it should not accept any parameters. You must declare all the parameters that you are planning to use in the constructor and set default values.

The simplest example of the contract that follows all these rules can be found here

NearBindgen decorator can accept requireInit parameter.

@NearBindgen({ requireInit: true })
class YourContract {
    ...
}

It is false by default, but if you will set it to true, it will prevent all the call functions from being executed before you initialize the state of the contract.

In order to initialize the contract, you need to add functions flagged with @initialize({}) decorator.

@call({}) decorator can accept two parameters: privateFunction and payableFunction. They are both false by default.

privateFunction: true can restrict access to this function to the contract itself.

payableFunction: true will allow the function to accept payments (deposit). Without this flag, it will panic if any deposit was provided.

Collections

A few useful on-chain persistent collections are provided. All keys, values and elements are of type Bytes.

Vector

Vector is an iterable implementation of vector that stores its content on the trie. Usage:

import {Vector} from 'near-sdk-js'

// in contract class constructor:
constructor() {
    super()
    this.v = new Vector('my_prefix_')
}

// Override the deserializer to load vector from chain
deserialize() {
    super.deserialize()
    this.v = Object.assign(new Vector, this.v)
}

someMethod() {
    // insert
    this.v.push('abc')
    this.v.push('def')
    this.v.push('ghi')

    // batch insert, extend:
    this.v.extend(['xyz', '123'])

    // get
    let first = this.v.get(0)

    // remove, move the last element to the given index
    this.v.swapRemove(0)

    // replace
    this.v.replace(1, 'jkl')

    // remove the last
    this.v.pop()

    // len, isEmpty
    let len = this.v.length
    let isEmpty = this.v.isEmpty()

    // iterate
    for (let element of this.v) {
        near.log(element)
    }

    // toArray, convert to JavaScript Array
    let a = this.v.toArray()

    // clear
    ths.v.clear()
}

LookupMap

LookupMap is an non-iterable implementation of a map that stores its content directly on the trie. It's like a big hash map, but on trie. Usage:

import {LookupMap} from 'near-sdk-js'

// in contract class constructor:
constructor() {
    super()
    this.m = new LookupMap('prefix_a')
}

// Override the deserializer to load vector from chain
deserialize() {
    super.deserialize()
    this.m = Object.assign(new LookupMap, this.m)
}

someMethod() {
    // insert
    this.m.set('abc', 'aaa')
    this.m.set('def', 'bbb')
    this.m.set('ghi', 'ccc')

    // batch insert, extend:
    this.m.extend([['xyz', '123'], ['key2', 'value2']])

    // check exist
    let exist = this.m.containsKey('abc')

    // get
    let value = this.m.get('abc')

    // remove
    this.m.remove('def')

    // replace
    this.m.set('ghi', 'ddd')
}

LookupSet

LookupSet is an non-iterable implementation of a set that stores its content directly on the trie. It's like LookupMap, but it only stores whether the value presents. Usage:

import {LookupSet} from 'near-sdk-js'

// in contract class constructor:
constructor() {
    super()
    this.s = new LookupSet('prefix_b')
}

// Override the deserializer to load vector from chain
deserialize() {
    super.deserialize()
    this.s = Object.assign(new LookupSet, this.s)
}

someMethod() {
    // insert
    this.s.set('abc')
    this.s.set('def')
    this.s.set('ghi')

    // batch insert, extend:
    this.s.extend(['xyz', '123'])

    // check exist
    let exist = this.s.contains('abc')

    // remove
    this.s.remove('def')
}

UnorderedMap

UnorderedMap is an iterable implementation of a map that stores its content directly on the trie. Usage:

import {UnorderedMap} from 'near-sdk-js'

// in contract class constructor:
constructor() {
    super()
    this.m = new UnorderedMap('prefix_c')
}

// Override the deserializer to load vector from chain
deserialize() {
    super.deserialize()
    this.m.keys = Object.assign(new Vector, this.m.keys)
    this.m.values = Object.assign(new Vector, this.m.values)
    this.m = Object.assign(new UnorderedMap, this.m)
}

someMethod() {
    // insert
    this.m.set('abc', 'aaa')
    this.m.set('def', 'bbb')
    this.m.set('ghi', 'ccc')

    // batch insert, extend:
    this.m.extend([['xyz', '123'], ['key2', 'value2']])

    // get
    let value = this.m.get('abc')

    // remove
    this.m.remove('def')

    // replace
    this.m.set('ghi', 'ddd')

    // len, isEmpty
    let len = this.m.length
    let isEmpty = this.m.isEmpty()

    // iterate
    for (let [k, v] of this.m) {
        near.log(k+v)
    }

    // toArray, convert to JavaScript Array
    let a = this.m.toArray()

    // clear
    this.m.clear()
}

UnorderedSet

UnorderedSet is an iterable implementation of a set that stores its content directly on the trie. It's like UnorderedMap but it only stores whether the value presents. Usage:

import {UnorderedSet} from 'near-sdk-js'

// in contract class constructor:
constructor() {
    super()
    this.s = new UnorderedSet('prefix_d')
}

// Override the deserializer to load vector from chain
deserialize() {
    super.deserialize()
    this.s.elements = Object.assign(new Vector, this.s.elements)
    this.s = Object.assign(new UnorderedSet, this.s)
}

someMethod() {
    // insert
    this.s.set('abc')
    this.s.set('def')
    this.s.set('ghi')

    // batch insert, extend:
    this.s.extend(['xyz', '123'])

    // check exist
    let exist = this.s.contains('abc')

    // remove
    this.s.remove('def')

    // len, isEmpty
    let len = this.s.length
    let isEmpty = this.s.isEmpty()

    // iterate
    for (let e of this.s) {
        near.log(e)
    }

    // toArray, convert to JavaScript Array
    let a = this.s.toArray()

    // clear
    this.s.clear()
}

Highlevel Promise APIs

Within a contract class that decorated by @Nearbindgen, you can work a high level JavaScript class, called NearPromise. It's equivalently expressive as promise batch APIs but much shorter to write and can be chained like a JavaScript Promise.

In a @call method, you can return either a JavaScript value or a NearPromise object. In the later case, @NearBindgen will automatically promiseReturn it for you.

Usage:

// create new promise
import { NearPromise, near, includeBytes } from "near-sdk-js";
import { PublicKey } from "near-sdk-js/lib/types";

let promise = NearPromise.new("account-to-run-promise");

// possible promise actions, choose and chain what you need:
promise
  .createAccount()
  .transfer(1_000_000_000_000_000_000_000_000_000_000_000_000n)
  .addFullAccessKey(new PublicKey(near.signerAccountPk()))
  .addAccessKey(
    new PublicKey(near.signerAccountPk()),
    250000000000000000000000n, // allowance
    "receiver_account_id",
    "allowed_function_names"
  )
  .stake(100000000000000000000000000000n, new PublicKey(near.signerAccountPk()))
  .deployContract(includeBytes("path/to/contract.wasm"))
  .functionCall(
    "callee_contract_account_id",
    inputArgs,
    0, // amount
    2 * Math.pow(10, 13) // gas
  )
  .functionCallWeight(
    "callee_contract_account_id",
    inputArgs,
    0, // amount
    2 * Math.pow(10, 13), // gas
    1 // weight
  )
  .deleteKey(new PublicKey(near.signerAccountPk()))
  .deleteAccount("beneficial_account_id");

return promise;

In the case of deploy contract, includeBytes is a helpful build-time util. You can include the content of a wasm contract, by using includeBytes('path/to/contract.wasm').

In the case of addFullAccessKey, addAccessKey and stake, it takes a PublicKey object, you can find more details about it in the Types sections below.

Besides above APIs to build something on top of an API, you can also chain promises with .then and .and, they're equivalent to promiseThen, promiseAnd:

// assume promise, promise2 and promise3 are create with above APIs, with several actions added like above.
promise.and(promise2).then(promise3); // promiseAnd of [promise_id, promise2_id], then promiseThen(promise_and_id, promise3_id)

return promise;

Types

NEAR-SDK-JS also includes type defintions that are equivalent to that in Rust SDK / nearcore. You can browse them in near-sdk-js/src/types. Most of them are just type alias to Bytes and bigint.

Public Key

Public Key is representing a NEAR account's public key in a JavaScript class. You can either initiate a Public Key from binary data, or from a human readable string.

The binary data is in the same format as nearcore, but encoded in bytes. That's one byte to represent the curve type of the public key, either ed25519 (\x00), or secp256k1 ('\x01'), follows by the curve-specific public key data in bytes. Examples:

new PublicKey(near.signerAccountPk());
new PublicKey(
  "\x00\xeb\x7f\x5f\x11\xd1\x08\x1f\xe0\xd2\x24\xc5\x67\x36\x21\xad\xcb\x97\xd5\x13\xff\xa8\x5e\x55\xbc\x2b\x74\x4f\x0d\xb1\xe9\xf8\x1f"
);
new PublicKey(
  "\x01\xf2\x56\xc6\xe6\xc8\x0b\x21\x3f\x2a\xa0\xb0\x17\x44\x23\x5d\x51\x5c\x59\x44\x35\xbe\x65\x1b\x15\x88\x3a\x10\xdd\x47\x2f\xa6\x46\xce\x62\xea\xf3\x67\x0d\xc5\xcb\x91\x00\xa0\xca\x2a\x55\xb2\xc1\x47\xc1\xe9\xa3\x8c\xe4\x28\x87\x8e\x7d\x46\xe1\xfb\x71\x4a\x99"
);

The human readable form is ed25519: or secp256k1: following base58-encoded public key. And initialize the Public Key with PublicKey.fromString:

PublicKey.fromString('ed25519:DXkVZkHd7WUUejCK7i74uAoZWy1w9AZqshhTHxhmqHuB`)
PublicKey.fromString('secp256k1:5r22SrjrDvgY3wdQsnjgxkeAbU1VcM71FYvALEQWihjM3Xk4Be1CpETTqFccChQr4iJwDroSDVmgaWZv2AcXvYeL`)

Once a PublicKey object is created, it can be used in high level promise APIs that takes a public key, such as addFullAccessKey, addAccessKey and stake.