n8n-code-javascript

JavaScript Code Node

Expert guidance for writing JavaScript code in n8n Code nodes.

Quick Start

// Basic template for Code nodes
const items = $input.all();

// Process data
const processed = items.map(item => ({
  json: {
    ...item.json,
    processed: true,
    timestamp: new Date().toISOString()
  }
}));

return processed;

Essential Rules

1. Choose "Run Once for All Items" mode (recommended for most use cases)
2. Access data: $input.all(), $input.first(), or $input.item
3. Return [{json: {...}}] — the canonical, mode-portable form. In Run Once for All Items mode n8n also auto-wraps a bare return {…} object, so that runs too; what genuinely fails is returning a primitive (string/number) or null.
4. CRITICAL: Webhook data is under $json.body (not $json directly)
5. Built-ins available: this.helpers.httpRequest() (no auth — the bare $helpers global is undefined in the task-runner sandbox, so $helpers.httpRequest() throws ReferenceError: $helpers is not defined), DateTime (Luxon), $jmespath(). Not available: this.helpers.httpRequestWithAuthentication (deny-listed), $env (when N8N_BLOCK_ENV_ACCESS_IN_NODE=true), require() (unless allowlisted). For anything beyond a trivial unauthenticated GET (auth, pagination, retries), prefer the HTTP Request node and keep Code nodes for pure logic.
6. Instance-allowlisted libraries: Self-hosted instances can allowlist modules via N8N_RUNNERS_ALLOWED_BUILT_IN_MODULES and N8N_RUNNERS_ALLOWED_EXTERNAL_MODULES (legacy: NODE_FUNCTION_ALLOW_BUILTIN / NODE_FUNCTION_ALLOW_EXTERNAL). If the user says their instance allows specific modules (e.g. axios, lodash, crypto), use them via require() — don't refuse. If unsure, ask or default to built-ins only.
7. Wrong skill? If you're writing code for a Custom Code Tool attached to an AI Agent (@n8n/n8n-nodes-langchain.toolCode), stop — that node has a different contract (input via query, must return a string, no $input/$helpers). Use the n8n-code-tool skill.