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Setting up a Flow Node with FCL: Simplifying Blockchain Development for Software Developers

In this article, we will explore how to develop a Flow node using FCL, providing code examples and links to relevant sources to guide you through the process.

Purple Dash
27/09/2023 7:22 AM

Table of Contents

Blockchain technology has gained immense popularity, offering a decentralized and secure infrastructure for various applications. Flow, a blockchain platform developed by Dapper Labs, stands out with its focus on scalability, developer-friendly environment, and unique smart contract architecture. To empower software developers and enable seamless integration with the Flow blockchain, the Flow Client Library (FCL) plays a crucial role. In this article, we will explore how to develop a Flow node using FCL, providing code examples and links to relevant sources to guide you through the process.

Understanding Flow and FCL

Flow is a fast, secure, and developer-friendly blockchain designed to support high-performance decentralized applications (dApps). With Flow, developers can create and deploy smart contracts, build dApps, and enable secure digital asset ownership and exchange. FCL, on the other hand, is a JavaScript library that simplifies the interaction between applications and the Flow blockchain.

Setting up the Development Environment

Before diving into developing a Flow node, we need to set up our development environment. Follow these steps:

  • Install Node.js: FCL is built using JavaScript, so make sure you have Node.js installed on your machine. You can download the latest version from the official Node.js website (https://nodejs.org).
  • Create a New Project: Open your terminal and create a new directory for your project. Navigate to the project directory and initialize a new Node.js project using the following command:
$ npm init -y
  • Install FCL: Now, install the FCL library by running the following command:
$ npm install @onflow/fcl

If using yarn, you can install the FCL library by running:

$ yarn add @onflow/fcl

Creating a Flow Node

With the development environment set up, let’s start building our Flow node using FCL. Follow these steps:

  • Import FCL: In your project’s entry file, import the FCL library as follows:
const fcl = require("@onflow/fcl");
  • Configure FCL: To establish a connection with the Flow blockchain, we need to configure FCL with the network information. “accessNode.api” accepts an API URL for the Flow Blockchain Access Node you want to communicate with; read more about the available endpoints here. Use the following code snippet as an example:
const config = {
"accessNode.api": "https://rest-testnet.onflow.org",
"discovery.wallet": "https://fcl-discovery.onflow.org/testnet/authn",
"flow.network": "testnet"

fcl.config().put("accessNode.api", config["accessNode.api"]);
fcl.config().put("discovery.wallet", config["discovery.wallet"]);
fcl.config().put("flow.network", config["flow.network"]);

You can learn more about common configuration keys passed to FCL here: https://developers.flow.com/tools/clients/fcl-js/api#setting-configuration-values

By default, the discovery endpoint will open an iframe overlay prompting the user to select and authenticate with a supported wallet. Once authenticated, the details of the active user will be stored in the CurrentUserObject for future reference and authentication.

  • Interacting with the Flow Blockchain: Once authenticated, we can interact with the Flow blockchain by sending transactions or executing scripts. The mutate method enables you to send transactions to the blockchain, with the potential to modify chain state. Here’s an example of sending a transaction:
const transactionId = await fcl.mutate({
  cadence: `
    transaction {
      execute {
        log("Hello, Flow!")
  proposer: fcl.currentUser,
  payer: fcl.currentUser,
  limit: 50

const transaction = await fcl.tx(transactionId).onceSealed();

Unlike many other blockchain systems, Flow allows for a separation between the entity initiating the transaction and the one covering its costs. Proposers and payers are specific types of authorizations that are mandatory for every transaction. The proposer’s role is akin to Ethereum’s nonce in transactions, serving as a safeguard against repeated attacks. The payer is the individual responsible for financing the transaction. If these roles are not explicitly defined, the Flow Client Library (FCL) defaults to using the current user for all transaction roles.

Further, we can use fcl.currentUser to authorize a transaction. Here’s an example of this using a prepare statement:

const transactionId = await fcl.mutate({
  cadence: `
    transaction {
      prepare(acct: AuthAccount) {
        log("Authorizing transaction")
      execute {
        log("Hello, Flow!")
  authorizations: [fcl.currentUser],
  limit: 50

const transaction = await fcl.tx(transactionId).onceSealed()

In this example, we pass 1 argument, fcl.currentUser, to the prepare statement. However, you can choose to pass more than one argument to the prepare statement if more authorizations are required; the arguments of the prepare statement correspond directly to the sequence of authorizations within the authorizations array.


In this article, we explored the process of developing with FCL. By leveraging FCL, software developers can seamlessly integrate their applications with the Flow blockchain, simplifying the development process and enabling a wide range of decentralized applications. We covered the setup of the development environment, the installation and configuration of FCL, and provided code examples to guide you through each step.

To further enhance your understanding and explore more advanced features, consider referring to the official Flow documentation (https://docs.onflow.org/). Experiment with different functionalities and leverage the power of Flow and FCL to build innovative decentralized applications that leverage the benefits of blockchain technology.

Remember, blockchain technology is continually evolving, and staying up to date with the latest advancements and best practices is crucial. Happy coding and exploring the world of decentralized applications with Flow and FCL!

Blockchain Development
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