title: Proper way of calling onChange function in React Final Form
body: <p>According to React Final Form documentation, I can pass onChange callback to <code>&lt;FormSpy /&gt;</code> component to execute code when form state changes. However, I also discovered that if I need to run some function every time when the form changes, I can also put this function inside Form's render callback before return statement:</p>
  <pre><code>&lt;Form
     onSubmit={onSubmit}
        render={({ handleSubmit }) =&gt; {
           myFunctionToRunOnChange(); // Call function here
           return (
              &lt;form onSubmit={handleSubmit}&gt;
                 &lt;div&gt;
                    &lt;label&gt;First Name&lt;/label&gt;
                    &lt;Field name=&quot;firstName&quot; component=&quot;input&quot; placeholder=&quot;First Name&quot; /&gt;
                 &lt;/div&gt;
                 &lt;button type=&quot;submit&quot;&gt;Submit&lt;/button&gt;
              &lt;/form&gt;
          );
     }}
  /&gt;
  </code></pre>
  <p>Is it good practice? For example, comparing with using FormSpy for onChange...</p>