Form Validation
Last updated: 2026-11-02
Form Validation Form Validation
The essence of validation is deriving errors from state: a validation function computes an errors object, the whole object is checked once before submitting, and when something is wrong the submit is blocked and the message is rendered. Error messages are UI too, so conditional rendering is enough — no imperative DOM work is required. Because the errors are computed while rendering, they can never drift out of sync with the fields they describe, which removes a whole class of stale-message bugs.
| Group | Component Patterns |
|---|---|
| Kind | Pattern |
ℹ️ Info The editor transpiles JSX to JavaScript and renders the real UI in a sandbox; components mount automatically — no manual render call needed.
📝 Syntax
const errors = validate(values) // derive errors from state
const hasError = Object.keys(errors).length > 0
<form onSubmit={e => {
e.preventDefault() // block the browser default submit
if (!hasError) submit(values)
}}>Returns：No return value; this entry describes an encoding pattern rather than a function.
▶ Example
The example runs out of the box: it auto-renders when expanded, and edits take effect instantly.
Output：
When the email is missing an @ or the password is shorter than 6 characters, clicking "Register" shows a red error under the matching field; once both are valid the page shows "Registered successfully".💡 Key Points
🏷️ More Component Patterns
💡 Related Cases
📚 Related Tutorials
❓ FAQ
