## Building the `generateProof.ts` Script: Setup and Dependencies This lesson guides you through the initial setup of the `generateProof.ts` script, a crucial component for generating zero-knowledge proofs in a JavaScript environment. We'll cover essential prerequisites, import necessary libraries, outline the script's logic, and organize our project files for clarity. ### Essential JavaScript Knowledge and Course Focus Before we dive into coding, it's important to address the prerequisites for the JavaScript-focused sections of this course. We'll be assuming a foundational understanding of several core JavaScript concepts: * **Objects:** Collections of key-value pairs. * **Classes:** Blueprints for creating objects, encapsulating data and functions. * **Methods:** Functions associated with objects or classes. * **Arrow functions:** A concise syntax for writing function expressions. * **Asynchronous functions (`async/await`):** For handling operations that don't complete immediately, such as file reading or network requests. * **Promises:** Objects representing the eventual completion (or failure) of an asynchronous operation and its resulting value. While we will offer very brief explanations as these concepts arise, this course is primarily focused on **Zero-Knowledge Proofs**—specifically, writing circuits and integrating them into applications. It is not designed to be an exhaustive JavaScript tutorial. If you need to strengthen your JavaScript skills, consider these resources: 1. **AI Agents:** Tools like ChatGPT are highly effective for explaining JavaScript concepts. 2. **Cyfrin Updraft Full-Stack Web3 Development Crash Course:** This comprehensive course (available at `updraft.cyfrin.io/courses/full-stack-web3-development-crash-course`) is recommended for a deeper dive into JavaScript, its mechanics, and frontend development. ### Importing Core Dependencies for `generateProof.ts` We'll now begin constructing our `generateProof.ts` script, located in the `js-scripts/` directory. The first step is to import the libraries that will provide the functionality we need. 1. **`Noir` from `@noir-lang/noir_js`**: This is the JavaScript library that allows us to interact with Noir circuits. Think of it as the JavaScript counterpart to Nargo (the Noir command-line tool and compiler), enabling us to compile, prove, and verify proofs programmatically within our JavaScript code. ```typescript import { Noir } from "@noir-lang/noir_js"; ``` 2. **`ethers` from `"ethers"`**: The `ethers` library is a widely-used toolkit for interacting with Ethereum and EVM-compatible blockchains. In our context, we'll primarily use it for ABI (Application Binary Interface) encoding, which helps in formatting data correctly for our circuit inputs. ```typescript import { ethers } from "ethers"; ``` 3. **`UltraHonkBackend` from `@aztec/bb.js`**: A zero-knowledge proof system requires a backend to handle the complex cryptographic operations involved in generating and verifying proofs. `UltraHonkBackend` is a specific implementation of a proving system (UltraPlonK with Honk arithmetization) that we will use. This is imported from the `bb.js` (Barretenberg.js) library, which provides WebAssembly bindings to the Barretenberg cryptographic library. ```typescript import { UltraHonkBackend } from "@aztec/bb.js"; ``` Your initial imports in `js-scripts/generateProof.ts` should look like this: ```typescript import { Noir } from "@noir-lang/noir_js"; import { ethers } from "ethers"; import { UltraHonkBackend } from "@aztec/bb.js"; ``` ### Outlining the Proof Generation Process To structure our `generateProof` script effectively, let's outline the high-level steps involved in generating a proof. We'll add these as comments in our code for now: ```typescript // get the circuit file with the bytecode // initialize Noir with the circuit // initialize the backend using the circuit bytecode // create the inputs // Execute the circuit with the inputs to create the witness // Generate the proof (using the backend) with the witness // return the proof ``` These steps represent the core logic we will implement: 1. **Retrieve Circuit Bytecode:** Load the compiled version of our Noir circuit. 2. **Initialize Noir:** Set up the `Noir` object with our circuit. 3. **Initialize Backend:** Prepare the `UltraHonkBackend` using the circuit's bytecode. 4. **Prepare Inputs:** Define and format the inputs for our specific circuit. 5. **Generate Witness:** Execute the circuit with the prepared inputs to compute all intermediate values (the witness). The witness is essential for proof generation. 6. **Generate Proof:** Use the backend and the witness to create the cryptographic proof. 7. **Return Proof:** Output the generated proof for verification or further use. ### Organizing Your Project: The `circuits` Directory Before proceeding with the implementation, it's good practice to organize our project structure. Currently, circuit-related files might be scattered. To improve clarity and maintainability, we'll consolidate them. 1. Create a new top-level folder in your project named **`circuits`**. 2. Move the following existing folders and files into this new `circuits` folder: * The `src` folder (which contains your `main.nr` Noir circuit code) * The `Nargo.toml` file (the Noir project manifest) * The `target` folder (which contains compiled circuit artifacts, including the bytecode) This organization keeps all circuit-specific source code, configuration, and build outputs neatly grouped together. ### Next Step: Accessing Circuit Bytecode With our dependencies imported and project structure organized, we are now ready to begin implementing the first step outlined: "get the circuit file with the bytecode specifically." This will be the focus of our next development phase.