Best Practices for Handling Attribution Tracking Fields in Marketo Forms

When working with attribution tracking fields in Marketo, there are a few key considerations to keep in mind to ensure accuracy, maintainability, and ease of debugging. A misconfigured form can lead to incorrect data, making it harder to track lead sources effectively.

Some best practices to avoid common pitfalls and keep your forms working smoothly.

1. Turn Off Pre-Fill for Attribution Tracking Fields

While Marketo’s Pre-Fill feature is useful in many cases, it’s best to turn it off for attribution fields. Why?

• When debugging, seeing an empty field (if no session data is provided) is far more transparent than mistakenly relying on old data.

• If a field isn't populated by the session context, leaving it blank ensures it won’t be overwritten with incorrect information.

• Marketo automatically ignores empty fields when posting to the database, so you don’t need to worry about accidental data loss.

2. Scope Element Selectors to the Marketo Form

When using JavaScript or jQuery to modify form elements, always scope your selectors to the specific Marketo <form> element instead of the entire document.

• Marketo allows multiple forms on a single page. If you apply changes at the document level, you risk modifying unintended forms.

• Keeping selectors scoped ensures that changes only affect the form they belong to, reducing unexpected behavior.

Example

Instead of:

document.querySelector("[name='utm_source']").value = "Google";

Use:

formElem.querySelector("[name='utm_source']").value = "Google";

(where formElem is the specific Marketo form instance).

3. Use the Forms API setValues() Instead of Direct DOM Updates

Marketo provides a Forms API that should always be used to update values, rather than directly modifying the DOM.

• Using setValues() ensures that visibility and validation rules stay intact.

• Directly changing DOM elements can break conditional logic or cause unexpected behavior in progressive profiling and field dependencies.

Correct Approach

MktoForms2.whenReady(function(form) { form.setValues({ "utm_source": "Google" }); });

This method keeps everything working as expected and prevents potential data inconsistencies.

TL;DR

Managing attribution fields in Marketo might seem like a small detail, but following these best practices can save you from data confusion, debugging headaches, and broken form behaviors.

By turning off Pre-Fill for tracking fields, scoping element selectors properly, and using the Forms API for value updates, you ensure your forms remain reliable, accurate, and easy to maintain.