Flatten Deeply Nested API Responses

Flatten a deeply nested API response with a single Code node instead of chaining Set nodes. Loop over the input items, read the nested values with optional chaining and nullish coalescing, and push a clean flat object for each record. This is common with Stripe, Shopify, and Salesforce webhooks, where values are buried several levels deep and expression-only extraction fails silently on missing keys.

Why flatten nested API responses in a Code node?

Many APIs return deeply nested JSON structures that are painful to work with in expression fields. Instead of chaining multiple Set nodes to extract nested values, use a single Code node to flatten the response into a clean, flat object. This is especially common with webhook payloads from Stripe, Shopify, and Salesforce.

Real-world example: A Stripe invoice.payment_succeeded webhook delivers line items buried three levels deep. Extracting them with expressions alone requires error-prone bracket notation and fails silently when keys are missing.

How do you flatten a nested response with a Code node?

// Mode: Run Once for All Items
const results = [];

for (const item of $input.all()) {
  const invoice = item.json;
  const lineItems = invoice?.data?.object?.lines?.data ?? [];

  for (const line of lineItems) {
    results.push({
      json: {
        invoiceId: invoice.data.object.id,
        customerId: invoice.data.object.customer,
        customerEmail: invoice.data.object.customer_email,
        lineDescription: line.description,
        amount: line.amount / 100,
        currency: line.currency.toUpperCase(),
        periodStart: new Date(line.period.start * 1000).toISOString(),
        periodEnd: new Date(line.period.end * 1000).toISOString(),
        priceId: line.price?.id ?? 'unknown',
        quantity: line.quantity ?? 1,
      }
    });
  }
}

return results;

This replaces what would otherwise be 5-6 Set and IF nodes, and handles missing keys safely with optional chaining and nullish coalescing.

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