Function node

Execute custom JavaScript functions in your workflow

Execute custom JavaScript functions deployed on Cloudflare Workers. Functions can process data, integrate with external APIs, and update workflow variables.

Configuration

• id: Unique node identifier
• function_id: ID of deployed function to execute
• save_response_to: Variable name to store function response (optional)

Function context

Kapso sends this JSON body to your function. Read it with await request.json():

{
  execution_context: {
    vars: {},      // Workflow variables
    system: {},    // System info (flow_id, started_at, etc)
    context: {}    // Channel info (phone_number, etc)
  },
  flow_events: [], // Recent workflow events (last 10)
  flow_info: {
    id: "flow_123",
    name: "Customer Support",
    step_id: "current_step_456"
  },
  whatsapp_context: { // Only if WhatsApp workflow
    conversation: {},
    messages: []
  }
}

Your function still uses the standard runtime signature:

async function handler(request, env) {
  const body = await request.json();
  const executionContext = body.execution_context || {};
  const vars = executionContext.vars || {};

  return new Response(JSON.stringify({
    vars: {
      normalized_email: (vars.email || "").trim().toLowerCase()
    }
  }), {
    headers: { "Content-Type": "application/json" }
  });
}

Function response

Functions can return JSON to update the workflow:

return new Response(JSON.stringify({
  vars: {
    user_score: 85,
    validated: true
  },
  next_edge: "success" // Optional: suggest next workflow path
}))

Functions can also emit project events:

return new Response(JSON.stringify({
  vars: {
    lead_score: 92
  },
  project_events: [
    {
      name: "lead.qualified",
      properties: {
        score: 92,
        source: "workflow"
      }
    }
  ]
}))

Project events follow the same validation rules as the Events API. A Function node response can emit at most 5 project events. See Events for limits and caveats.

How it works

1. Invokes function: Calls your deployed function with workflow context
2. Processes response: Updates workflow variables from function response
3. Continues workflow: Advances to next step via next edge
4. Saves data: Optionally stores full response in specified variable

Usage patterns

Data validation

API integration

Conditional processing

Workflow library example

Use function slugs in local workflow source. kapso push resolves the slug to the Platform API function_id.

workflow.addNode("normalize_phone", {
  type: "function",
  functionSlug: "normalize-phone",
  saveResponseTo: "normalized_phone"
});