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Transfer tokens

Transfer tokens cross-chain

There are two ways to transfer tokens cross-chain with Axelar:

  1. Call sendToken on an Axelar gateway EVM contract.
  2. Get a deposit address using the AxelarJS SDK.

Use sendToken if:

  • Your app transfers EVM-to-X where X is one of EVM, Cosmos.
  • Your app uses smart contracts.

Use a deposit address if:

  • You need functionality not offered by sendToken. Example: Cosmos-to-X.
  • You want to allow token transfers from wallets that don't know anything about Axelar. Example: Withdrawal from a centralized exchange.

Call sendToken

Overview

  1. Locate the Axelar Gateway contract on the source chain
  2. Execute approve on the source chain (ERC-20)
  3. Execute sendToken on the Gateway

1. Locate the Axelar Gateway contract on the source chain

Axelar Gateways are application-layer smart contracts established on source and destination chains. They send and receive payloads, and monitor state. Find a list of gateway addresses for the chains we support in Resources [Mainnet | Testnet | Testnet-2].

An Axelar Gateway implements the IAxelarGateway interface, which has a public method called sendToken:

function sendToken(
    string memory destinationChain,
    string memory destinationAddress,
    string memory symbol,
    uint256 amount
) external;

2. Execute approve on the source chain (ERC-20)

Transferring tokens through a Gateway is similar to an ERC-20 token transfer. You first need to approve the Gateway to transfer a specific token in a specific amount. This approval is done via the approve method of the ERC-20 interface:

function approve(address spender, uint256 amount) external returns (bool);

Here spender is the Gateway address on the source chain.

Find a list of assets, their names and their addresses in Resources [Mainnet | Testnet | Testnet-2].

3. Execute sendToken on the Gateway

Call sendToken on the gateway contract of the source chain. Example:

sendToken(
    "avalanche", // destination chain name
    "0xF16DfB26e1FEc993E085092563ECFAEaDa7eD7fD", // some destination wallet address (should be your own)
    "USDC", // asset symbol
    100000000 // amount (in atomic units)
)

Watch for the tokens to appear at the destination address on the destination chain.

Get a deposit address

A deposit address is a special address created and monitored by Axelar relayer services. It is similar to how centralized exchanges generate a monitored one-time deposit address that facilitate your token transfers.

Deposit address workflow:

  1. Generate a deposit address.
  2. User sends tokens to the deposit address. Examples: withdrawal from a centralized exchange, transaction from your favorite wallet software.
  3. Axelar relayers observe the transaction on the source chain and complete it on the destination chain.

Install the AxelarJS SDK

We'll use the AxelarJS SDK, which is a npm dependency that empowers developers to make requests into the Axelar network from a frontend. The Axelar SDK provides a wrapper for API calls that you can use to generate a deposit address. (Alternately, see Send UST to an EVM chain for an example of how to generate a deposit address using the CLI instead of the Axelar SDK.)

Install the Axelar SDK:

npm i @axelar-network/axelarjs-sdk@alpha

(We recommend installing the alpha version as the stable version is now legacy. The alpha version is scalable and uses websockets to wait for the deposit address generation.)

Generate a deposit address using the SDK

Call getDepositAddress:

async getDepositAddress(
  fromChain: string, // source chain
  toChain: string, // destination chain
  destinationAddress: string, // destination address to transfer the token to
  asset: string, // common key of the asset
  options?: {
    _traceId: string;
  }
): Promise<string> {}

Example: Cosmos-to-EVM (Terra to Avalanche):

const sdk = new AxelarAssetTransfer({
  environment: "testnet",
  auth: "local",
});
const depositAddress = await sdk.getDepositAddress(
  "terra", // source chain
  "avalanche", // destination chain
  "0xF16DfB26e1FEc993E085092563ECFAEaDa7eD7fD", // destination address
  "uusd" // asset to transfer
);

Example: EVM-to-Cosmos (Avalanche to Terra)

const sdk = new AxelarAssetTransfer({
  environment: "testnet",
  auth: "local",
});
const depositAddress = await sdk.getDepositAddress(
  "avalanche", // source chain
  "terra", // destination chain
  "terra1qem4njhac8azalrav7shvp06myhqldpmkk3p0t", // destination address
  "uusd" // asset to transfer
);

Note: The destination address format is validated based on the destination chain. Make sure that the destination address is a valid address on the destination chain. For instance Terra addresses start with “terra,” Osmosis with “osmo,” etc.

Once the deposit address has been generated the user can make a token transfer (on blockchain) to the deposit address. The transfer will be picked up by the Axelar network and relayed to the destination chain.

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