Function node - Kapso Documentation

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)

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"
});

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

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

Usage patterns

Data validation API integration Conditional processing

​Configuration

​Workflow library example

​Function context

​Function response

​How it works

​Usage patterns