@twobirds/microcomponents/public/documentation/observables.md

Micro Components Organization Class

![logo](./MicroComponents.svg)

# Observables

This module provides utilities for observing and binding data to DOM elements using placeholders. It supports reactive updates when data changes.

## Table of Contents

- [Overview](#overview)
- [Functions](#functions)
- [Types](#types)
- [Example](#example)

---

## Overview

The module defines an `observe` function that makes object properties observable.

You can use this function to turn a single property or all properties of an object into observables.

This functionality can be used standalone in any framework.

## Functions

### `observe( target: LooseObject, propertyName?: string ): LooseObject`

**Description**  

Registers a distinct property or all object properties as an observable, making them reactive.

Those properties are dual use: 

- **Direct Assign Native Values**:  
  - Directly assign native values to the property, and the observable will be notified of the change and its callbacks will be run.

- **Use as an Instance of Observable**
  - Use the property as an instance of the `Observable` class. This allows you to attach callbacks and react to changes. You can bind the property to DOM elements.

## Types

### `Observable`

**Type**  
```typescript
export type Observable = {
  observe: (cb: Callback) => void; // attach a callback to be notified of changes
  notify: () => void; // mostly internal use, but can be called to trigger all callbacks
  bind: (target: HTMLElement | DocumentFragment | ShadowRoot) => void; // the target DOM element to bind the observable to. {placeholder} will be replaced with the actual data value.
};
```

**Methods**

- `observe(cb: Callback)`  
  Registers a callback to be notified of changes.

- `notify( enable?: boolean)`
  - Enables / Disables notifications.
  - By default, notifications are enabled.
  - If `enable` is `false`, notifications are disabled. You need to explicitly call `notify(true)` to re-enable notifications.
  - Otherwise calls all registered callbacks with the current data.

- `bind(target: HTMLElement | DocumentFragment | ShadowRoot)`  
  Binds the observable to a DOM element, replacing placeholders with data values.


## Example

HTML:
```html
<div id="user-card">
  <p>Hello, {name}</p>
  <p>Age: {age}</p>
</div>
```

JavaScript:
```javascript
import { observe } from './observables.js';

const data = {
  name: 'John',
  age: 30,
};

observe(data); // all properties of the data object will be observed.

const element = document.getElementById('user-card');
data.bind(element);
```

When `data.name` or `data.age` changes, the DOM updates automatically.

---

## Notes

- Only objects can be bound to the DOM.
- Native values (strings, numbers, booleans) are wrapped in observable proxies.
- Changes to observable properties trigger updates in bound DOM elements.