Form Actions
All Svelte topics∙ Svelte
Form Actions explains a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson. You will learn its exact Svelte rule, failure mode, verification plan, and production evidence.
Syntax
export const actions = { default: async ({ request }) => ({ success: true }) };Example
// Topic: Form Actions
const action = { validates: true, authorized: true };
console.log(action.validates && action.authorized ? 'saved' : 'rejected');
// Expected Output: savedExpected Output
savedLine-by-line
| Line | Meaning |
|---|---|
const action = { validates: true, authorized: true }; | Defines state, behavior, or output for this Svelte example. |
console.log(action.validates && action.authorized ? 'saved' : 'rejected'); | Prints the expected result for this Svelte lesson. |
Real-World Uses
- 1Form Actions is used for full-stack Svelte applications with SSR and deployment adapters.
- 2Its mechanism is a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson.
- 3Use actions for reusable DOM behavior with explicit parameter and cleanup contracts. Keep decisions specific to form, actions.
- 4Production code must account for An action that mutates unrelated application state becomes hidden coupling. Do not copy assumptions from a neighboring topic into form, actions.
- 5Teams evaluate it using DOM behavior reuse and cleanup measured for form, actions.
Common Mistakes
- 1An action that mutates unrelated application state becomes hidden coupling. Do not copy assumptions from a neighboring topic into form, actions.
- 2Implementing Form Actions without understanding a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson.
- 3Choosing Form Actions where simpler local Svelte code is clearer.
- 4Skipping Test initialization, parameter update, event dispatch, and destroy. Include an assertion that directly exercises form, actions.
- 5Optimizing before measuring DOM behavior reuse and cleanup measured for form, actions.
Best Practices
- 1Use actions for reusable DOM behavior with explicit parameter and cleanup contracts. Keep decisions specific to form, actions.
- 2Document a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson in the smallest useful component, store, action, route, or service.
- 3Represent every relevant loading, success, empty, denied, and failure state.
- 4Test initialization, parameter update, event dispatch, and destroy. Include an assertion that directly exercises form, actions.
- 5Use DOM behavior reuse and cleanup measured for form, actions to guide improvements.
How it works
- 1Form Actions relies on a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson.
- 2Use actions for reusable DOM behavior with explicit parameter and cleanup contracts. Keep decisions specific to form, actions.
- 3Its main failure mode is An action that mutates unrelated application state becomes hidden coupling. Do not copy assumptions from a neighboring topic into form, actions.
- 4Useful evidence is DOM behavior reuse and cleanup measured for form, actions.
Implementation decisions
- 1Identify the owning component, store, action, route, load function, or server handler.
- 2Keep state local until multiple owners genuinely need it.
- 3Keep server secrets and validation outside browser components.
- 4Define cleanup for subscriptions, actions, timers, and requests.
Verification plan
- 1Test initialization, parameter update, event dispatch, and destroy. Include an assertion that directly exercises form, actions.
- 2Check initial render, assignment-driven updates, user interaction, and cleanup.
- 3Confirm keyboard and screen-reader behavior for visible UI.
- 4Measure production output only after correctness passes.
Practice task
- 1Build the smallest Form Actions example.
- 2Introduce this failure: An action that mutates unrelated application state becomes hidden coupling. Do not copy assumptions from a neighboring topic into form, actions.
- 3Correct it using this rule: Use actions for reusable DOM behavior with explicit parameter and cleanup contracts. Keep decisions specific to form, actions.
- 4Record DOM behavior reuse and cleanup measured for form, actions before and after the change.
Quick Summary
- Form Actions works through a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson.
- Use actions for reusable DOM behavior with explicit parameter and cleanup contracts. Keep decisions specific to form, actions.
- Avoid An action that mutates unrelated application state becomes hidden coupling. Do not copy assumptions from a neighboring topic into form, actions.
- Test initialization, parameter update, event dispatch, and destroy. Include an assertion that directly exercises form, actions.
- Measure success with DOM behavior reuse and cleanup measured for form, actions.
Interview Questions
Q1. What is Form Actions used for?
Answer: It is used for full-stack Svelte applications with SSR and deployment adapters.
Q2. How does Form Actions work in Svelte?
Answer: It works through a use directive function attached to a DOM element with optional update and destroy for this form, actions lesson.
Q3. What rule matters most?
Answer: Use actions for reusable DOM behavior with explicit parameter and cleanup contracts. Keep decisions specific to form, actions.
Q4. What failure is common?
Answer: An action that mutates unrelated application state becomes hidden coupling. Do not copy assumptions from a neighboring topic into form, actions.
Q5. How should it be verified?
Answer: Test initialization, parameter update, event dispatch, and destroy. Include an assertion that directly exercises form, actions. Evaluate DOM behavior reuse and cleanup measured for form, actions.
Quiz
Which practice best supports Form Actions?