If the component re-render, prevValues will be an empty object and the calculated values will the be broken

[jdeniau]

What is the current behavior?

If a hook make the component re-render, then the prevValues will be an empty object and the "updates" function are triggered even if the values did not change

What is the expected behavior?

The "update" function should probably not be triggered, but they are probably because the prevValues is an empty object, which should not happen either

Sandbox Link

My current fix

const decorator = createDecorator({
  field: 'foo',
  updates:  (fieldValue, fieldName, allValues, prevValues) => {
    if (typeof prevValues[fieldName] === 'undefined') {
      return {};
    }

    // do real stuff
  }
})

Extracted from the final-form-calculate example: https://codesandbox.io/s/react-final-form-calculated-fields-forked-wpm4f?file=/index.js

What's your environment?

• final-form: 4.12.0
• final-form-calculate: 1.3.2
• react-final-form: 5.0.1