Instructions on running Node JavaScript code in n8n

Most users know n8n as a no-code automation platform – drag and drop nodes, connect applications, and run workflows without writing a single line of code. But in reality, that's only a fraction of the tool's power.

When faced with more complex problems – handling nested structured data, custom computations, calling external libraries, or integrating specific business logic – you need more than what the built-in nodes can do. This is where the JavaScript node code in n8n comes into play.

JavaScript is the native language of n8n , offering optimal performance and perfect compatibility. Combined with the launch of n8n 2.0 and its Task Runners , which isolate the execution environment and reduce the risk of arbitrary code, this is the best time to learn how to leverage JavaScript right within your workflow .

How to add and configure JavaScript code nodes in n8n

Step 1: Open the workflow and add a new node.

Access n8n and open the workflow you are working on (or create a new workflow). Click the "Add" button on the canvas to open the node search panel.

Step 2: Select the Core group and find the Code node.

In the node search table, select the "Core" tab to filter core nodes. Find and select the node named "Code," then select "Code in JavaScript. " This node allows you to run custom code directly in the workflow.

Step 3: Choose the JavaScript language

After adding the Code node to the canvas, open the configuration panel. You will see the "Language" section – the system defaults to "JavaScript" . If it is in a different language, click on it and change it back to JavaScript.

To date, n8n has optimized the V8 engine within its standalone Task Runners, resulting in significantly faster and smoother performance for array and string processing tasks using JavaScript Code Node.

Step 4: Select Execution Mode

Before writing code, choose the Mode that best suits your needs:

1. Run Once for All Items: This option runs the code only once, and all data from the previous node is passed in as a list. This is suitable when you need to process large datasets or perform aggregate calculations.
2. Run Once for Each Item: This executes the code repeatedly for each individual item. It's suitable when each record needs to be processed independently.

Step 5: Write JavaScript code

In the code input area, you can access data from previous nodes through the variable $input.

1. When using the "Run Once for All Items" mode:

JavaScript

const items = $input.all(); const total = items.reduce( ( sum, item ) => sum + (item.json.amount || 0 ), 0 ); return [{ json : { total : total, count : items.length } }];

1. When using the "Run Once for Each Item" mode:

JavaScript

const item = $input.item; const name = item.json.name || '' ; return { json : { name_uppercase : name.toUpperCase(), length : name.length } };

Step 6: Execution and testing

Click "Execute Step" to test the node with real data from the previous node. The right-hand panel will immediately display the output, allowing you to verify that the code is working correctly before connecting to the next nodes.

Things you can actually do with JavaScript in n8n

Handling complex data that the available nodes cannot handle.

1. Node.js, available in n8n, is excellent for normalization operations. But when you need to handle multi-level nested JSON strings, perform advanced array functions ( map, filter, reduce), or convert date and time formats according to complex rules – JavaScript is the natural choice. You can use the full power of built-in objects like Math, Date, JSON, RegExpimmediately without further configuration.

Integrating JavaScript into AI workflows

1. In the current technological landscape, organizations and individuals are using n8n not only for simple automation but also for complex AI workflows integrating multiple processing steps. JavaScript code nodes play a crucial role in this chain: cleaning input data before sending it to the AI ​​agent, formatting complex JSON structures for more efficient prompting, or parsing output from the LLM before saving it to the database.

Practical advantages and disadvantages

Advantage

1. No external infrastructure required: The entire logic resides directly within the workflow – significantly reducing infrastructure complexity and potential errors compared to maintaining an external serverless function.
2. Maximum execution speed (Native): Because n8n is built on the Node.js platform, JavaScript runs directly at peak performance without the environment startup lag (cold start) that occurs when calling other asynchronous languages.
3. Excellent Editor and Auto-Complete Support: n8n provides strong support for JavaScript with its code suggestion system (autocomplete), visually displaying helper functions and input data structures, making coding very easy.
4. Security is improved in n8n 2.x: The Task Runners feature isolates the custom code execution environment, completely eliminating the risk of leaks or hangs in the main n8n system process.

Disadvantages

1. Third-party libraries are limited by default: You cannot freely install external NPM packages into Code Node. To use external libraries, you are required to configure NODE_FUNCTION_ALLOW_EXTERNALthe n8n system environment variables.
2. Not suitable for very simple tasks: If you only need to concatenate two strings or rename basic data fields, using a Code node is overkill. Nodes like Edit Fields or Set perform this task much more intuitively and quickly.

Conclude

The JavaScript code node in n8n is a crucial bridge between no-code automation and programmatic data processing. It helps you break free from the limitations of drag-and-drop interfaces, providing absolute flexibility to handle any type of data structure as desired.

With continuous improvements from n8n 2.0 to the present, JavaScript support has become increasingly stable, secure, and performance-optimized. If you are building large, complex workflows and need a robust layer of customizable logic, take advantage of JavaScript as your secret weapon in your n8n toolkit.