Using transform-data steps

Transform-data steps manipulate data using JavaScript in a sandboxed environment, letting you format, filter, merge, or calculate values within Flows.

Add a transform step

1. In the Flow editor, click Add Step
2. Select Transform Data
3. Configure:
   • Name: Descriptive label (e.g., “Format response”)
   • Script: Write your JavaScript transformation logic
   • Output Variable: Name for the result variable
4. Click Save Step

Writing scripts

Write JavaScript that returns a value. All Flow variables from previous steps are available directly by their outputVariable name:

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// Access a variable called "customer_data" from a prior step
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const formatted = {
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  name: customer_data.name.toUpperCase(),
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  email: customer_data.email.toLowerCase(),
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  timestamp: new Date().toISOString()
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};
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return formatted;

Reference output from earlier steps by their outputVariable name:

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const summary = generate_summary; // outputVariable from a prior prompt step
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const wordCount = summary.split(' ').length;
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return {
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  summary: summary,
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  wordCount: wordCount,
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  readingTime: Math.ceil(wordCount / 200) + ' minutes'
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};

Common transformations

Array operations

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// Filter and map array — "order_data" is an outputVariable from a prior step
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const highValueOrders = order_data.orders
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  .filter(order => order.amount > 1000)
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  .map(order => ({
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    id: order.id,
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    total: order.amount,
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    formattedTotal: '$' + order.amount.toFixed(2)
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  }));
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return highValueOrders;

Object merging

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// Combine data from multiple sources — reference outputVariable names directly
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return {
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  ...customer_data,
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  ...order_history,
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  enrichedAt: new Date().toISOString()
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};

String formatting

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// "contact_info" is an outputVariable from a prior step
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const name = contact_info.firstName + ' ' + contact_info.lastName;
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const slug = name.toLowerCase().replace(/\s+/g, '-');
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return { name, slug };

Calculations

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// "cart" is an outputVariable from a prior step
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const items = cart.items;
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const subtotal = items.reduce((sum, item) => sum + item.price, 0);
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const tax = subtotal * 0.08;
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const total = subtotal + tax;
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return { subtotal, tax, total };

Available JavaScript features

Transform steps run in a sandboxed environment (Cloudflare Worker by default) and support modern JavaScript:

• Array methods (map, filter, reduce, etc.)
• Destructuring and spread operators
• Arrow functions
• Template literals
• async/await
• Date objects
• Math functions
• JSON.parse and JSON.stringify
• Built-in helper utilities (available under helpers.*)

External libraries are not available in the default sandbox. Use API call steps for external data.

The default step timeout is 5 minutes. Keep transformations focused to avoid unnecessary execution time.

Error handling

Wrap risky operations in try/catch:

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try {
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  const parsed = JSON.parse(raw_data);
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  return { success: true, data: parsed };
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} catch (error) {
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  return { success: false, error: error.message };
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}

Testing transformations

Use the step tester to validate logic:

1. Click Test on the transform step
2. Provide sample input
3. Review output
4. Iterate until correct

Best practices

• Keep it simple: Complex logic belongs in external services
• Name clearly: Use descriptive step names that explain the transformation
• Handle nulls: Check for undefined/null values before accessing properties
• Return consistent types: Always return the same structure for predictability

Next steps

• Flow variables and templates for variable reference
• Using conditional steps for logic based on transformed data
• Using fetch-url and api-call steps for external data