feat: set field errors from the form validators

docs/framework/react/guides/validation.md

@@ -194,6 +194,109 @@ export default function App() {
 }
 ```
 
+### Setting field-level errors from the form's validators
+
+You can set errors on the fields from the form's validators. One common use case for this is validating all the fields on submit by calling a single API endpoint in the form's `onSubmitAsync` validator.
+
+```tsx
+export default function App() {
+  const form = useForm({
+    defaultValues: {
+      age: 0,
+    },
+    validators: {
+      onSubmitAsync: async ({ value }) => {
+        // Verify the age on the server
+        const isOlderThan13 = await verifyAgeOnServer(value.age)
+        if (!isOlderThan13) {
+          return {
+            form: 'Invalid data', // The `form` key is optional
+            fields: {
+              age: 'Must be 13 or older to sign',
+            },
+          }
+        }
+
+        return null
+      },
+    },
+  })
+
+  return (
+    <div>
+      <form
+        onSubmit={(e) => {
+          e.preventDefault()
+          e.stopPropagation()
+          void form.handleSubmit()
+        }}
+      >
+        <form.Field name="age">
+          {(field) => (
+            <>
+              <label htmlFor={field.name}>Age:</label>
+              <input
+                id={field.name}
+                name={field.name}
+                value={field.state.value}
+                type="number"
+                onChange={(e) => field.handleChange(e.target.valueAsNumber)}
+              />
+              {field.state.meta.errors ? (
+                <em role="alert">{field.state.meta.errors.join(', ')}</em>
+              ) : null}
+            </>
+          )}
+        </form.Field>
+        <form.Subscribe
+          selector={(state) => [state.errorMap]}
+          children={([errorMap]) =>
+            errorMap.onSubmit ? (
+              <div>
+                <em>There was an error on the form: {errorMap.onSubmit}</em>
+              </div>
+            ) : null
+          }
+        />
+        {/*...*/}
+      </form>
+    </div>
+  )
+}
+```
+
+> Something worth mentioning is that if you have a form validation function that returns an error, that error may be overwritten by the field-specific validation.
+>
+> This means that:
+>
+> ```jsx
+>  const form = useForm({
+>     defaultValues: {
+>       age: 0,
+>     },
+>     validators: {
+>       onChange: ({ value }) => {
+>         return {
+>           fields: {
+>             age: value.age < 12 ? 'Too young!' : undefined,
+>           },
+>         }
+>       },
+>     },
+> })
+>
+> // ...
+>
+> return <form.Field
+>   name="age"
+>   validators={{
+>     onChange: ({ value }) => value % 2 === 0 ? 'Must be odd!' : undefined,
+>   }}
+> />
+> ```
+>
+> Will only show `'Must be odd!` even if the 'Too young!' error is returned by the form-level validation.
+
 ## Asynchronous Functional Validation
 
 While we suspect most validations will be synchronous, there are many instances where a network call or some other async operation would be useful to validate against.

examples/react/field-errors-from-form-validators/.eslintrc.cjs

@@ -0,0 +1,11 @@
+// @ts-check
+
+/** @type {import('eslint').Linter.Config} */
+const config = {
+  extends: ['plugin:react/recommended', 'plugin:react-hooks/recommended'],
+  rules: {
+    'react/no-children-prop': 'off',
+  },
+}
+
+module.exports = config

examples/react/field-errors-from-form-validators/.gitignore

@@ -0,0 +1,27 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+
+# testing
+/coverage
+
+# production
+/build
+
+pnpm-lock.yaml
+yarn.lock
+package-lock.json
+
+# misc
+.DS_Store
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*

examples/react/field-errors-from-form-validators/README.md

@@ -0,0 +1,6 @@
+# Example
+
+To run this example:
+
+- `npm install`
+- `npm run dev`

examples/react/field-errors-from-form-validators/index.html

@@ -0,0 +1,18 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <link rel="icon" type="image/svg+xml" href="/emblem-light.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <meta name="theme-color" content="#000000" />
+
+    <title>
+      TanStack Form React Field Errors From Form Validators Example App
+    </title>
+  </head>
+  <body>
+    <noscript>You need to enable JavaScript to run this app.</noscript>
+    <div id="root"></div>
+    <script type="module" src="/src/index.tsx"></script>
+  </body>
+</html>

examples/react/field-errors-from-form-validators/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "@tanstack/field-errors-from-form-validators",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite --port=3001",
+    "build": "vite build",
+    "preview": "vite preview",
+    "test:types": "tsc"
+  },
+  "dependencies": {
+    "@tanstack/react-form": "^0.29.2",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1"
+  },
+  "devDependencies": {
+    "@types/react": "^18.3.3",
+    "@types/react-dom": "^18.3.0",
+    "@vitejs/plugin-react": "^4.3.1",
+    "vite": "^5.4.2"
+  },
+  "browserslist": {
+    "production": [
+      ">0.2%",
+      "not dead",
+      "not op_mini all"
+    ],
+    "development": [
+      "last 1 chrome version",
+      "last 1 firefox version",
+      "last 1 safari version"
+    ]
+  }
+}

examples/react/field-errors-from-form-validators/src/index.tsx

@@ -0,0 +1,134 @@
+import { useForm } from '@tanstack/react-form'
+import * as React from 'react'
+import { createRoot } from 'react-dom/client'
+
+async function sleep(ms: number) {
+  return new Promise((resolve) => {
+    setTimeout(resolve, ms)
+  })
+}
+
+async function verifyAgeOnServer(age: number) {
+  await sleep(Math.floor(Math.random() * 1000))
+  return age <= 13
+}
+
+async function checkIfUsernameIsTaken(name: string) {
+  await sleep(Math.floor(Math.random() * 500))
+  const usernames = ['user-1', 'user-2', 'user-3']
+  return !usernames.includes(name)
+}
+
+export default function App() {
+  const form = useForm({
+    defaultValues: {
+      username: '',
+      age: 0,
+    },
+    validators: {
+      onSubmitAsync: async ({ value }) => {
+        const [isRightAge, isUsernameAvailable] = await Promise.all([
+          // Verify the age on the server
+          verifyAgeOnServer(value.age),
+          // Verify the availability of the username on the server
+          checkIfUsernameIsTaken(value.username),
+        ])
+
+        if (!isRightAge || !isUsernameAvailable) {
+          return {
+            // The `form` key is optional
+            form: 'Invalid data',
+            fields: {
+              ...(!isRightAge ? { age: 'Must be 13 or older to sign' } : {}),
+              ...(!isUsernameAvailable
+                ? { username: 'Username is taken' }
+                : {}),
+            },
+          }
+        }
+
+        return null
+      },
+    },
+  })
+
+  return (
+    <div>
+      <h1>Field Errors From The Form's validators Example</h1>
+      <form
+        onSubmit={(e) => {
+          e.preventDefault()
+          e.stopPropagation()
+          void form.handleSubmit()
+        }}
+      >
+        <form.Field
+          name="username"
+          validators={{
+            onSubmit: ({ value }) => (!value ? 'Required field' : null),
+          }}
+          children={(field) => (
+            <div>
+              <label htmlFor={field.name}>Username:</label>
+              <input
+                id={field.name}
+                name={field.name}
+                value={field.state.value}
+                onChange={(e) => {
+                  field.handleChange(e.target.value)
+                }}
+              />
+              {field.state.meta.errors.length > 0 ? (
+                <em role="alert">{field.state.meta.errors.join(', ')}</em>
+              ) : null}
+            </div>
+          )}
+        />
+
+        <form.Field
+          name="age"
+          validators={{
+            onSubmit: ({ value }) => (!value ? 'Required field' : null),
+          }}
+          children={(field) => (
+            <div>
+              <label htmlFor={field.name}>Age:</label>
+              <input
+                id={field.name}
+                name={field.name}
+                value={field.state.value}
+                type="number"
+                onChange={(e) => field.handleChange(e.target.valueAsNumber)}
+              />
+              {field.state.meta.errors.length > 0 ? (
+                <em role="alert">{field.state.meta.errors.join(', ')}</em>
+              ) : null}
+            </div>
+          )}
+        />
+        <form.Subscribe
+          selector={(state) => [state.errorMap]}
+          children={([errorMap]) =>
+            errorMap.onSubmit ? (
+              <div>
+                <em>There was an error on the form: {errorMap.onSubmit}</em>
+              </div>
+            ) : null
+          }
+        />
+        <form.Subscribe
+          selector={(state) => [state.canSubmit, state.isSubmitting]}
+          children={([canSubmit, isSubmitting]) => (
+            <button type="submit" disabled={!canSubmit}>
+              {isSubmitting ? '...' : 'Submit'}
+            </button>
+          )}
+        />
+      </form>
+    </div>
+  )
+}
+
+const rootElement = document.getElementById('root')!
+
+createRoot(rootElement).render(<App />)

examples/react/field-errors-from-form-validators/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "compilerOptions": {
+    "jsx": "react",
+    "noEmit": true,
+    "strict": true,
+    "esModuleInterop": true,
+    "lib": ["DOM", "DOM.Iterable", "ES2020"]
+  }
+}