180 lines
5.0 KiB
Markdown
180 lines
5.0 KiB
Markdown
# Reactive Branching: `$if( )`
|
|
|
|
The `$if` function is a reactive control flow operator. It manages the conditional rendering of components with optional smooth transitions, ensuring that only the active branch exists in the DOM and in memory.
|
|
|
|
## Function Signature
|
|
|
|
```typescript
|
|
$if(
|
|
condition: Signal<boolean> | Function,
|
|
thenVal: Component | Node,
|
|
otherwiseVal?: Component | Node,
|
|
transition?: Transition
|
|
): HTMLElement
|
|
```
|
|
|
|
| Parameter | Type | Required | Description |
|
|
| :--- | :--- | :--- | :--- |
|
|
| **`condition`** | `Signal` | Yes | A reactive source that determines which branch to render. |
|
|
| **`thenVal`** | `any` | Yes | The content to show when the condition is **truthy**. |
|
|
| **`otherwiseVal`** | `any` | No | The content to show when the condition is **falsy** (defaults to null). |
|
|
| **`transition`** | `Transition` | No | Optional animation hooks for enter/exit transitions. |
|
|
|
|
**Returns:** A `div` element with `display: contents` that acts as a reactive portal for the branches.
|
|
|
|
---
|
|
|
|
## Transition Interface
|
|
|
|
```typescript
|
|
interface Transition {
|
|
/** Called when branch enters. Use for fade-in, slide-in, etc. */
|
|
in: (el: HTMLElement) => void;
|
|
/** Called when branch leaves. Call `done()` when animation completes. */
|
|
out: (el: HTMLElement, done: () => void) => void;
|
|
}
|
|
```
|
|
|
|
### Example: Fade Transition
|
|
|
|
```javascript
|
|
const fade = {
|
|
in: (el) => {
|
|
el.style.opacity = "0";
|
|
el.style.transition = "opacity 0.3s";
|
|
requestAnimationFrame(() => {
|
|
el.style.opacity = "1";
|
|
});
|
|
},
|
|
out: (el, done) => {
|
|
el.style.transition = "opacity 0.3s";
|
|
el.style.opacity = "0";
|
|
setTimeout(done, 300);
|
|
}
|
|
};
|
|
|
|
$if(show, Modal, null, fade);
|
|
```
|
|
|
|
---
|
|
|
|
## Usage Patterns
|
|
|
|
### 1. Simple Toggle
|
|
|
|
```javascript
|
|
const isVisible = $(false);
|
|
|
|
Div([
|
|
Button({ onclick: () => isVisible(!isVisible()) }, "Toggle Message"),
|
|
|
|
$if(isVisible,
|
|
P("Now you see me!"),
|
|
P("Now you don't...")
|
|
)
|
|
]);
|
|
```
|
|
|
|
### 2. With Smooth Animation
|
|
|
|
```javascript
|
|
const showModal = $(false);
|
|
|
|
Div([
|
|
Button({ onclick: () => showModal(true) }, "Open Modal"),
|
|
|
|
$if(showModal,
|
|
() => Modal({ onClose: () => showModal(false) }),
|
|
null,
|
|
fade // ← Smooth enter/exit animation
|
|
)
|
|
]);
|
|
```
|
|
|
|
### 3. Lazy Component Loading
|
|
|
|
Unlike CSS `display: none`, `$if` is **lazy**. The inactive branch is never created, saving memory.
|
|
|
|
```javascript
|
|
$if(() => user.isLogged(),
|
|
() => Dashboard(), // Only executed if logged in
|
|
() => LoginGate() // Only executed if guest
|
|
)
|
|
```
|
|
|
|
### 4. Complex Conditions
|
|
|
|
```javascript
|
|
$if(() => count() > 10 && status() === 'ready',
|
|
Span("Threshold reached!")
|
|
)
|
|
```
|
|
|
|
### 5. $if.not Helper
|
|
|
|
```javascript
|
|
$if.not(loading,
|
|
() => Content(), // Shows when loading is FALSE
|
|
() => Spinner() // Shows when loading is TRUE
|
|
)
|
|
```
|
|
|
|
---
|
|
|
|
## Automatic Cleanup
|
|
|
|
One of the core strengths of `$if` is its integrated **Cleanup** logic. SigPro ensures that when a branch is swapped out, it is completely purged.
|
|
|
|
1. **Stop Watchers**: All `$watch` calls inside the inactive branch are permanently stopped.
|
|
2. **Unbind Events**: Event listeners attached via `$html` are removed.
|
|
3. **Recursive Sweep**: SigPro performs a deep "sweep" of the removed branch.
|
|
4. **Transition Respect**: When using transitions, destruction only happens AFTER the `out` animation completes.
|
|
|
|
---
|
|
|
|
## Best Practices
|
|
|
|
- **Function Wrappers**: For heavy components, use `() => MyComponent()` to prevent initialization until needed.
|
|
- **Reusable Transitions**: Define common transitions (fade, slide, scale) in a shared module.
|
|
- **Cleanup**: No manual cleanup needed. SigPro handles everything automatically.
|
|
|
|
---
|
|
|
|
## Technical Comparison
|
|
|
|
| Feature | Standard CSS `hidden` | SigPro `$if` |
|
|
| :--- | :--- | :--- |
|
|
| **DOM Presence** | Always present | Only if active |
|
|
| **Reactivity** | Still processing | **Paused/Destroyed** |
|
|
| **Memory usage** | Higher | **Optimized** |
|
|
| **Cleanup** | Manual | **Automatic** |
|
|
| **Smooth Transitions** | Manual | **Built-in hook** |
|
|
| **Animation Timing** | You manage | **Respected by core** |
|
|
|
|
---
|
|
|
|
## Complete Transition Examples
|
|
|
|
### Fade
|
|
```javascript
|
|
const fade = {
|
|
in: (el) => { el.style.opacity = "0"; requestAnimationFrame(() => { el.style.transition = "opacity 0.3s"; el.style.opacity = "1"; }); },
|
|
out: (el, done) => { el.style.transition = "opacity 0.3s"; el.style.opacity = "0"; setTimeout(done, 300); }
|
|
};
|
|
```
|
|
|
|
### Slide
|
|
```javascript
|
|
const slide = {
|
|
in: (el) => { el.style.transform = "translateX(-100%)"; requestAnimationFrame(() => { el.style.transition = "transform 0.3s"; el.style.transform = "translateX(0)"; }); },
|
|
out: (el, done) => { el.style.transition = "transform 0.3s"; el.style.transform = "translateX(-100%)"; setTimeout(done, 300); }
|
|
};
|
|
```
|
|
|
|
### Scale
|
|
```javascript
|
|
const scale = {
|
|
in: (el) => { el.style.transform = "scale(0)"; requestAnimationFrame(() => { el.style.transition = "transform 0.2s"; el.style.transform = "scale(1)"; }); },
|
|
out: (el, done) => { el.style.transition = "transform 0.2s"; el.style.transform = "scale(0)"; setTimeout(done, 200); }
|
|
};
|
|
``` |