fix: update form props on render

docs/guides/basic-concepts.md

@@ -0,0 +1,218 @@
+---
+id: basic-concepts
+title: Basic Concepts and Terminology
+---
+
+# Basic Concepts and Terminology
+
+This page introduces the basic concepts and terminology used in the @tanstack/react-form library. Familiarizing yourself with these concepts will help you better understand and work with the library.
+
+## Form Factory
+
+The Form Factory is responsible for creating form instances with a shared configuration. It is created using the `createFormFactory` function, which accepts a configuration object with default values for the form fields. This shared configuration allows you to create multiple form instances with consistent behavior.
+
+Example:
+
+```tsx
+const formFactory = createFormFactory<Person>({
+  defaultValues: {
+    firstName: '',
+    lastName: '',
+    hobbies: [],
+  },
+})
+```
+
+## Form Instance
+
+A Form Instance is an object that represents an individual form and provides methods and properties for working with the form. You create a form instance using the useForm hook provided by the form factory. The hook accepts an object with an onSubmit function, which is called when the form is submitted.
+
+```tsx
+const form = formFactory.useForm({
+  onSubmit: async (values) => {
+    // Do something with form data
+    console.log(values)
+  },
+})
+```
+
+## Field
+
+A Field represents a single form input element, such as a text input or a checkbox. Fields are created using the form.Field component provided by the form instance. The component accepts a name prop, which should match a key in the form's default values. It also accepts a children prop, which is a render prop function that takes a field object as its argument.
+
+Example:
+
+```tsx
+<form.Field
+  name="firstName"
+  children={(field) => (
+    <>
+      <input {...field.getInputProps()} />
+      <FieldInfo field={field} />
+    </>
+  )}
+/>
+```
+
+## Field State
+
+Each field has its own state, which includes its current value, validation status, error messages, and other metadata. You can access a field's state using the field.state property.
+
+Example:
+
+```tsx
+const { value, error, touched, isValidating } = field.state
+```
+
+## Field API
+
+The Field API is an object passed to the render prop function when creating a field. It provides methods for working with the field's state, such as getInputProps, which returns an object with props needed to bind the field to a form input element.
+
+Example:
+
+```tsx
+<input {...field.getInputProps()} />
+```
+
+## Validation
+
+@tanstack/react-form provides both synchronous and asynchronous validation out of the box. Validation functions can be passed to the form.Field component using the validate and validateAsync props.
+
+Example:
+
+```tsx
+<form.Field
+  name="firstName"
+  validate={(value) => !value && 'A first name is required'}
+  validateAsync={async (value) => {
+    await new Promise((resolve) => setTimeout(resolve, 1000))
+    return value.includes('error') && 'No "error" allowed in first name'
+  }}
+  children={(field) => (
+    <>
+      <input {...field.getInputProps()} />
+      <FieldInfo field={field} />
+    </>
+  )}
+/>
+```
+
+## Reactivity
+
+@tanstack/react-form offers various ways to subscribe to form and field state changes, such as the form.useStore hook, the form.Subscribe component, and the form.useField hook. These methods allow you to optimize your form's rendering performance by only updating components when necessary.
+
+Example:
+
+```tsx
+<form.Subscribe
+  selector={(state) => [state.canSubmit, state.isSubmitting]}
+  children={([canSubmit, isSubmitting]) => (
+    <button type="submit" disabled={!canSubmit}>
+      {isSubmitting ? '...' : 'Submit'}
+    </button>
+  )}
+/>
+```
+
+## Array Fields
+
+Array fields allow you to manage a list of values within a form, such as a list of hobbies. You can create an array field using the form.Field component with the mode="array" prop. The component accepts a children prop, which is a render prop function that takes an arrayField object as its argument.
+
+When working with array fields, you can use the fields `pushValue`, `removeValue`, and `swapValues` methods to add, remove, and swap values in the array.
+
+Example:
+
+```tsx
+<form.Field
+  name="hobbies"
+  mode="array"
+  children={(hobbiesField) => (
+    <div>
+      Hobbies
+      <div>
+        {!hobbiesField.state.value.length
+          ? 'No hobbies found.'
+          : hobbiesField.state.value.map((_, i) => (
+              <div key={i}>
+                <hobbiesField.Field
+                  index={i}
+                  name="name"
+                  children={(field) => {
+                    return (
+                      <div>
+                        <label htmlFor={field.name}>Name:</label>
+                        <input name={field.name} {...field.getInputProps()} />
+                        <button
+                          type="button"
+                          onClick={() => hobbiesField.removeValue(i)}
+                        >
+                          X
+                        </button>
+                        <FieldInfo field={field} />
+                      </div>
+                    )
+                  }}
+                />
+                <hobbiesField.Field
+                  index={i}
+                  name="description"
+                  children={(field) => {
+                    return (
+                      <div>
+                        <label htmlFor={field.name}>Description:</label>
+                        <input name={field.name} {...field.getInputProps()} />
+                        <FieldInfo field={field} />
+                      </div>
+                    )
+                  }}
+                />
+              </div>
+            ))}
+      </div>
+      <button
+        type="button"
+        onClick={() =>
+          hobbiesField.pushValue({
+            name: '',
+            description: '',
+            yearsOfExperience: 0,
+          })
+        }
+      >
+        Add hobby
+      </button>
+    </div>
+  )}
+/>
+```
+
+## Array-Nested Fields
+
+Rendering fields that are items of a nested array require only a small change to the `form.Field` component props.
+
+Example:
+
+```tsx
+<hobbiesField.Field
+  index={i}
+  name="name"
+  children={(field) => {
+    return (
+      <div>
+        <label htmlFor={field.name}>Name:</label>
+        <input name={field.name} {...field.getInputProps()} />
+        <button type="button" onClick={() => hobbiesField.removeValue(i)}>
+          X
+        </button>
+        <FieldInfo field={field} />
+      </div>
+    )
+  }}
+/>
+```
+
+These are the basic concepts and terminology used in the @tanstack/react-form library. Understanding these concepts will help you work more effectively with the library and create complex forms with ease.
+
+```
+
+```

packages/form-core/src/FormApi.ts

@@ -148,7 +148,9 @@ export class FormApi<TFormData> {
     this.update(opts || {})
   }
 
-  update = (options: FormOptions<TFormData>) => {
+  update = (options?: FormOptions<TFormData>) => {
+    if (!options) return
+
     this.store.batch(() => {
       if (
         options.defaultState &&

packages/react-form/src/useForm.tsx

@@ -57,6 +57,8 @@ export function useForm<TData>(opts?: FormOptions<TData>): FormApi<TData> {
     return api
   })
 
+  formApi.update(opts)
+
   return formApi as any
 }