83 lines
3.0 KiB
Markdown
83 lines
3.0 KiB
Markdown
# Reactive Lists: `For( )`
|
|
|
|
The `For` function is a high-performance list renderer. It maps an array (or a Signal containing an array) to DOM nodes. Unlike a simple `.map()`, `For` is **keyed**, meaning it only updates, moves, or deletes the specific items that changed.
|
|
|
|
## Function Signature
|
|
|
|
```typescript
|
|
For(
|
|
source: Signal<any[]> | Function | any[],
|
|
render: (item: any, index: number) => HTMLElement,
|
|
keyFn?: (item: any, index: number) => string | number
|
|
): HTMLElement
|
|
```
|
|
|
|
| Parameter | Type | Required | Description |
|
|
| :--- | :--- | :--- | :--- |
|
|
| **`source`** | `Signal` | Yes | The reactive array to iterate over. |
|
|
| **`render`** | `Function` | Yes | A function that returns a component or Node for each item. |
|
|
| **`keyFn`** | `Function` | **No** | A function to extract a **unique ID**. If omitted, it defaults to the `index`. |
|
|
|
|
**Returns:** A `div` element with `display: contents` containing the live list.
|
|
|
|
---
|
|
|
|
## Usage Patterns
|
|
|
|
### 1. Basic Keyed List (Recommended)
|
|
Always use a unique property (like an `id`) as a key to ensure SigPro doesn't recreate nodes unnecessarily when reordering or filtering.
|
|
|
|
```javascript
|
|
const users = $([
|
|
{ id: 1, name: "Alice" },
|
|
{ id: 2, name: "Bob" }
|
|
]);
|
|
|
|
Ul({ class: "list" }, [
|
|
For(users,
|
|
(user) => Li({ class: "p-2" }, user.name),
|
|
(user) => user.id // Stable and unique key
|
|
)
|
|
]);
|
|
```
|
|
|
|
### 2. Simplified Usage (Automatic Key)
|
|
If you omit the third parameter, `For` will automatically use the array index as the key. This is ideal for simple lists that don't change order frequently.
|
|
|
|
```javascript
|
|
const tags = $(["Tech", "JS", "Web"]);
|
|
|
|
// No need to pass keyFn if the index is sufficient
|
|
Div({ class: "flex gap-1" }, [
|
|
For(tags, (tag) => Badge(tag))
|
|
]);
|
|
```
|
|
|
|
---
|
|
|
|
## How it Works (The Reconciliation)
|
|
|
|
When the `source` signal changes, `For` performs the following steps:
|
|
|
|
1. **Key Diffing**: It compares the new keys with the previous ones stored in an internal `Map`.
|
|
2. **Node Reuse**: If a key already exists, the DOM node is **reused** and moved to its new position. No new elements are created.
|
|
3. **Physical Cleanup**: If a key disappears from the list, SigPro calls `.destroy()` to stop reactivity and physically removes the node from the DOM to prevent memory leaks.
|
|
|
|
---
|
|
|
|
## Performance Tips
|
|
|
|
* **Stable Keys**: Never use `Math.random()` as a key. This will force SigPro to destroy and recreate the entire list on every update, killing performance.
|
|
* **State Preservation**: If your list items have internal state (like an input with text), `For` ensures that state is preserved even if the list is reordered, as long as the key (`id`) remains the same.
|
|
|
|
---
|
|
|
|
## Summary Comparison
|
|
|
|
| Feature | Standard `Array.map` | SigPro `For` |
|
|
| :--- | :--- | :--- |
|
|
| **Re-render** | Re-renders everything | Only updates changes |
|
|
| **DOM Nodes** | Re-created every time | **Reused via Keys** |
|
|
| **Memory** | Potential leaks | **Automatic Cleanup** |
|
|
| **State** | Lost on re-render | **Preserved per item** |
|
|
| **Ease of Use** | Manual logic required | **Optional (fallback to index)** | |