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This example performs the simplest cross-contract call possible: it calls our Hello NEAR example to set and retrieve a greeting. It is one of the simplest examples on making a cross-contract call, and the perfect gateway to the world of interoperative contracts.
Advanced Cross-Contract Calls Check the tutorial on how to perform cross-contract calls in batches and in parallel

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Clone the Example

You have two options to start the project:
  1. You can use the app through Github Codespaces, which will open a web-based interactive environment.
  2. Clone the repository locally and use it from your computer.
CodespacesClone locally
Open in GitHub Codespaces🌐 https://github.com/near-examples/cross-contract-calls

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Structure of the Example

The smart contract is available in two flavors: Rust and JavaScript 
┌── sandbox-ts # sandbox testing
│    ├── hello-near
│    │    └── hello-near.wasm
│    └── main.ava.ts
├── src # contract's code
│    └── contract.ts
├── package.json
├── README.md
└── tsconfig.json

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Smart Contract

The contract exposes methods to query the greeting and change it. These methods do nothing but calling get_greeting and set_greeting in the hello-near example.

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Querying for the Greeting

The contract performs a cross-contract call to hello.near-example.testnet to get the greeting message, and then handles the response in a callback function.

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Callback Function

The callback function processes the result of the cross-contract call. In this case, it simply returns the greeting message obtained from the hello-near contract. Notice that the callback function is marked as private, meaning it can only be called by the contract itself.

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Testing the Contract

The contract readily includes a set of unit and sandbox testing to validate its functionality. To execute the tests, run the following commands: 
cd contract-simple-ts
yarn
yarn test
The integration tests use a sandbox to create NEAR users and simulate interactions with the contract.
In this project in particular, the integration tests first deploy the hello-near contract. Then, they test that the cross-contract call correctly sets and retrieves the message. You will find the integration tests in sandbox-ts/ for the JavaScript version and in tests/ for the Rust version.

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Deploying the Contract to the NEAR network

In order to deploy the contract you will need to create a NEAR account. 
# Create a new account pre-funded by a faucet
near create-account <accountId> --useFaucet
Go into the directory containing the smart contract (cd contract-advanced-ts or cd contract-advanced-rs), build and deploy it: 
npm run build
near deploy <accountId> ./build/cross_contract.wasm --initFunction new --initArgs '{"hello_account":"hello.near-example.testnet"}'

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CLI: Interacting with the Contract

To interact with the contract through the console, you can use the following commands: 
# Get message from the hello-near contract
# Replace <accountId> with your account ID
near call <accountId> query_greeting --useAccount <accountId>

# Set a new message for the hello-near contract
# Replace <accountId> with your account ID
near call <accountId> change_greeting '{"new_greeting":"XCC Hi"}' --useAccount <accountId>

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Moving Forward

A nice way to learn is by trying to expand a contract. Modify the cross contract example to use the guest-book contract!. In this way, you can try to make a cross-contract call that attaches money. Remember to correctly handle the callback, and to return the money to the user in case of error.

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Advanced Cross Contract Calls

Your contract can perform multiple cross-contract calls in simultaneous, creating promises that execute in parallel, or as a batch transaction. Check the advanced cross contract calls tutorial to learn more.
Versioning for this articleAt the time of this writing, this example works with the following versions:
  • near-cli: 4.0.13
  • node: 18.19.1
  • rustc: 1.77.0