npm package: @mmstack/primitives
Description: A collection of utility functions and primitives designed to enhance development with Angular Signals, providing helpful patterns and inspired by features from other reactive libraries. All value helpers also use pure derivations (no effects/RxJS).
Latest version: 21.0.20

# @mmstack/primitives

A collection of utility functions and primitives designed to enhance development with Angular Signals, providing helpful patterns and inspired by features from other reactive libraries. All value helpers also use pure derivations (no effects/RxJS).

[![npm version](https://badge.fury.io/js/%40mmstack%2Fprimitives.svg)](https://badge.fury.io/js/%40mmstack%2Fprimitives)
[![License](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/mihajm/mmstack/blob/master/packages/primitives/LICENSE)

## Installation

```bash
npm install @mmstack/primitives
```

## Primitives

This library provides the following primitives:

- `debounced` - Creates a writable signal whose value updates are debounced after set/update.
- `throttled` - Creates a writable signal whose value updates are rate-limited.
- `mutable` - A signal variant allowing in-place mutations while triggering updates.
- `stored` - Creates a signal synchronized with persistent storage (e.g., localStorage).
- `piped` – Creates a signal with a chainable & typesafe `.pipe(...)` method, which returns a pipable computed.
- `store` - A deep-reactivity proxy, with Array & Record support.
- `withHistory` - Enhances a signal with a complete undo/redo history stack.
- `indexArray` - Maps a reactive array by index into an array of stable derivations.
- `keyArray` - Maps a reactive array by key (track by) into an array of stable derivations.
- `mapObject` - Maps a reactive object by key (track by) into an object of stable derivations.
- `nestedEffect` - Creates an effect with a hierarchical lifetime, enabling fine-grained, conditional side-effects.
- `toWritable` - Converts a read-only signal to writable using custom write logic.
- `derived` - Creates a signal with two-way binding to a source signal.
- `chunked` - Creates a signal that time-slices an array into chunked values & emits thats array based on the provided options.
- `tabSync` - Low level primitive to "share" the value of a WritableSignal accross tabs via the BroadcastChannel api.
- `sensor` - A facade function to create various reactive sensor signals (e.g., mouse position, network status, page visibility, dark mode preference)." (This was the suggestion from before; it just reads a little smoother and more accurately reflects what the facade creates directly).
  - `mediaQuery` - A generic primitive that tracks a CSS media query (forms the basis for `prefersDarkMode` and `prefersReducedMotion`).
  - `elementVisibility` - Tracks if an element is intersecting the viewport using IntersectionObserver.
  - `elementSize` - Tracks the size of the DOM element
  - `mediaQuery` - Creates a signal that reacts to changes based on the provided media queries "truthyness". Additional helpers such as `prefersDarkMode` and `prefersReducedMotion` available
  - `mousePosition` - Throttled signal that reacts to the mouses position within a given element
  - `networkStatus` - A signal of the current network status, used my @mmstack/resource
  - `pageVisibility` - A signal useful when reacting to the user switching tabs
  - `scrollPosition` - A throttled signal of the current scroll position within a given element
  - `windowSize` - A throttled signal useful to reacting to window resize events
- `until` - Creates a Promise that resolves when a signal's value meets a specific condition.

---

### debounced

Creates a WritableSignal where the propagation of its value (after calls to .set() or .update()) is delayed. The publicly readable signal value updates only after a specified time (ms) has passed without further set/update calls. It also includes an .original property, which is a Signal reflecting the value immediately after set/update is called.

```typescript
import { Component, signal, effect } from '@angular/core';
import { debounced, debounce } from '@mmstack/primitives';
import { FormsModule } from '@angular/forms';

@Component({
  selector: 'app-debounced',
  template: `<input [(ngModel)]="searchTerm" />`,
})
export class SearchComponent {
  searchTerm = debounced('', { ms: 300 }); // Debounce for 300ms
  example2 = debounce(signal(''), { ms: 300 }); // pattern for adding debounce to an existing signal

  constructor() {
    effect(() => {
      // Runs 300ms after the user stops typing
      console.log('Perform search for:', this.searchTerm());
    });
    effect(() => {
      // Runs immediately on input change
      console.log('Input value:', this.searchTerm.original());
    });
  }
}
```

You can also debounce an existing signal:

```typescript
import { debounce } from '@mmstack/primitives';

const query = signal('');
const debouncedQuery = debounce(query, { ms: 300 });
```

### throttled

Creates a WritableSignal whose value is rate-limited. It ensures that the public-facing signal only updates at most once per specified time interval (ms). It uses a trailing-edge strategy, meaning it updates with the most recent value at the end of the interval. This is useful for handling high-frequency events like scrolling or mouse movement without overwhelming your application's reactivity.

```typescript
import { Component, signal, effect } from '@angular/core';
import { throttled } from '@mmstack/primitives';
import { JsonPipe } from '@angular/common';

@Component({
  selector: 'app-throttle-demo',
  standalone: true,
  imports: [JsonPipe],
  template: `
    <div (mousemove)="onMouseMove($event)" style="width: 300px; height: 200px; border: 1px solid black; padding: 10px; user-select: none;">Move mouse here to see updates...</div>
    <p><b>Original Position:</b> {{ position.original() | json }}</p>
    <p><b>Throttled Position:</b> {{ position() | json }}</p>
  `,
})
export class ThrottleDemoComponent {
  // Throttle updates to at most once every 200ms
  position = throttled({ x: 0, y: 0 }, { ms: 200 });

  constructor() {
    // This effect runs on every single mouse move event.
    effect(() => {
      // console.log('Original value updated:', this.position.original());
    });
    // This effect will only run at most every 200ms.
    effect(() => {
      console.log('Throttled value updated:', this.position());
    });
  }

  onMouseMove(event: MouseEvent) {
    this.position.set({ x: event.offsetX, y: event.offsetY });
  }
}
```

### mutable

Creates a MutableSignal, a signal variant designed for scenarios where you want to perform in-place mutations on objects or arrays held within the signal, while still ensuring Angular's change detection is correctly triggered. It provides .mutate() and .inline() methods alongside the standard .set() and .update(). Please note that any computeds, which resolve non-primitive values from a mutable require equals to be set to false.

```typescript
import { Component, computed, effect } from '@angular/core';
import { mutable } from '@mmstack/primitives';
import { FormsModule } from '@angular/forms';

@Component({
  selector: 'app-mutable',
  template: ` <button (click)="incrementAge()">inc</button> `,
})
export class SearchComponent {
  user = mutable({ name: { first: 'John', last: 'Doe' }, age: 30 });

  constructor() {
    effect(() => {
      // Runs every time user is mutated
      console.log(this.user());
    });

    const age = computed(() => this.user().age);

    effect(() => {
      // Runs every time age changes
      console.log(age());
    });

    const name = computed(() => this.user().name);
    effect(() => {
      // Doesnt run if user changes, unless name is destructured
      console.log(name());
    });

    const name2 = computed(() => this.user().name, {
      equal: () => false,
    });

    effect(() => {
      // Runs every time user changes (even if name did not change)
      console.log(name2());
    });
  }

  incrementAge() {
    user.mutate((prev) => {
      prev.age++;
      return prev;
    });
  }

  incrementInline() {
    user.inline((prev) => {
      prev.age++;
    });
  }
}
```

### stored

Creates a WritableSignal whose state is automatically synchronized with persistent storage (like localStorage or sessionStorage), providing a fallback value when no data is found or fails to parse.

It handles Server-Side Rendering (SSR) gracefully, allows dynamic storage keys, custom serialization/deserialization, custom storage providers, and optional synchronization across browser tabs via the storage event. It returns a StoredSignal<T> which includes a .clear() method and a reactive .key signal.

```typescript
import { Component, effect, signal } from '@angular/core';
import { stored } from '@mmstack/primitives';
// import { FormsModule } from '@angular/forms'; // Needed for ngModel

@Component({
  selector: 'app-theme-selector',
  standalone: true,
  // imports: [FormsModule], // Import if using ngModel
  template: `
    Theme:
    <select [value]="theme()" (change)="theme.set($event.target.value)">
      <option value="light">Light</option>
      <option value="dark">Dark</option>
      <option value="system">System</option>
    </select>
    <button (click)="theme.clear()">Reset Theme</button>
    <p>Using storage key: {{ theme.key() }}</p>
  `,
})
export class ThemeSelectorComponent {
  // Persist theme preference in localStorage, default to 'system'
  theme = stored<'light' | 'dark' | 'system'>('system', {
    key: 'user-theme',
    syncTabs: true, // Sync theme choice across tabs
  });

  constructor() {
    effect(() => {
      console.log(`Theme set to: ${this.theme()}`);
      // Logic to apply theme (e.g., add class to body)
      document.body.className = `theme-${this.theme()}`;
    });
  }
}
```

### piped

Adds two fluent APIs to signals:

- **`.map(...transforms, [options])`** – compose pure, synchronous value→value transforms. Returns a computed signal that remains pipeable.
- **`.pipe(...operators)`** – compose operators (signal→signal), useful for combining signals or reusable projections.

```typescript
import { piped, pipeable, select, combineWith } from '@mmstack/primitives';
import { signal } from '@angular/core';

const count = piped(1);

// Map: value -> value
const label = count.map(
  (n) => n * 2,
  (n) => (num: n),
  { equal: (a, b) => a.num === b.num },
);

// Pipe: signal -> signal
const base = pipeable(signal(10));
const total = count.pipe(select((n) => n * 3)).pipe(combineWith(count, (a, b) => a + b));

label(); // e.g., "#2"
total(); // reactive sum
```

### store / mutableStore / toStore

Provides "Deep Reactivity" by creating a proxy around a source object or array. Instead of reading raw values, accessing a property on a store returns a Signal representing that specific property.
This allows you to pass specific slices of a large state object to child components as Input() signals, or bind directly to nested properties without manually creating computed or derived selectors.
Propagates mutablity/writability down the chain so if the source is a WritableSignal all children are WritableSignal derivations.

#### Features:

- Lazy Generation: Sub-signals are created only when accessed.
- Caching: Accessed signals are cached (via WeakRef), so accessing state.user.name multiple times returns the exact same signal instance.
- Array Support: Array signals provide reactive access to indices (e.g., state.users[0])

```ts
import { Component, effect } from '@angular/core';
import { store, mutableStore } from '@mmstack/primitives';
import { FormsModule } from '@angular/forms';
import { JsonPipe } from '@angular/common';

@Component({
  selector: 'app-store-demo',
  standalone: true,
  imports: [FormsModule, JsonPipe],
  template: `
    <h3>User Profile</h3>
    <p>Name: {{ state.user.name() }}</p>

    <input [ngModel]="state.user.name()" (ngModelChange)="state.user.name.set($event)" />

    <h3>Settings (Mutable)</h3>
    <label>
      <input type="checkbox" [checked]="settings.notifications.email()" (change)="toggleEmail()" />
      Email Notifications
    </label>

    <pre>{{ state() | json }}</pre>
  `,
})
export class StoreDemoComponent {
  // 1. Standard Store
  state = store({
    user: {
      name: 'Alice',
      address: { city: 'New York', zip: 10001 },
    },
    tags: ['admin', 'editor'],
  });

  // 2. Mutable Store (allows .mutate/.inline)
  settings = mutableStore({
    theme: 'dark',
    notifications: { email: true, sms: false },
  });

  constructor() {
    // Effect tracks only the specific slice accessed
    effect(() => {
      console.log('City changed to:', this.state.user.address.city());
    });

    // Array access returns a signal for that index
    const firstTag = this.state.tags[0];
    console.log('First tag:', firstTag()); // 'admin'
  }

  updateZip() {
    // You can set deep properties directly
    this.state.user.address.zip.set(90210);
  }

  toggleEmail() {
    // With mutableStore, you can use .mutate on the root or sub-signals
    this.settings.notifications.mutate((n) => {
      n.email = !n.email;
    });
  }
}
```

### Array Stores

When a store holds an array, the array itself is a signal, but you can also access indices as signals. Additionally Array stores also expose a `.length` signal & support Symbol.Iterator.
Currently the array store function isn't exposed, but they are automatically created when a given property within the store is an array. Hit me up, if you need top-level array support, though in those cases you're probably looking for `indexArray` / `keyArray`

```ts
const state = store({
  todos: [
    { id: 1, text: 'Buy Milk', done: false },
    { id: 2, text: 'Walk Dog', done: true },
  ],
});

const firstTodo = state.todos[0]; // Signal<{ text: string, ... }>
const firstTodoText = state.todos[0].text; // Signal<string>

// Update specific item property without replacing the whole array
state.todos[0].done.set(true);

const len = state.todos.length(); // reacts to length changes

for (const todo of state.todos) {
  const t = todo(); // iteration returns proxied children
  const id = todo.id();
}
```

### indexArray/keyArray

Reactive map helper that stabilizes a source array Signal by length. It provides stability by giving the mapping function a stable Signal<T> for each item based on its index. Sub signals are not re-created, rather they propagate value updates through. This is particularly useful for rendering lists (@for) as it minimizes DOM changes when array items change identity but represent the same conceptual entity.

`keyArray` is similar, but stabilizes/reconciles via a provided track by function instead of the index. This is computationally more expensive, so use it when "identity" stability is more important than simply data pass-through

Both utilize memory pooling to "ease" GC pressure.

```typescript
import { Component, signal } from '@angular/core';
import { indexArray, keyArray, mutable } from '@mmstack/primitives';

@Component({
  selector: 'app-map-demo',
  template: `
    <ul>
      @for (item of displayItems(); track item) {
        <li>{{ item() }}</li>
        @if ($first) {
            <button (click)="updateFirst(item)">Update First</button>
        }
      }
    </ul>
    <button (click)="addItem()">Add</button>
  `,
})
export class ListComponent {
  readonly sourceItems = signal([
    { id: 1, name: 'A' },
    { id: 2, name: 'B' },
  ]);

  readonly displayItems = indexArray(this.sourceItems, (child, index) => computed(() => `Item ${index}: ${child().name}`));

  // keyArray is similar, but the index becomes dynamic & the child object is static
  readonly keyed = keyArray(this.sourceItems, (child, index) => computed(() => `Item ${index()}: ${child.name}}`), {
    key: (item) => item.id
  });


  addItem() {
    this.sourceItems.update((items) => [...items, { id: Date.now(), name: String.fromCharCode(67 + items.length - 2) }]);
  }

  updateFirst() {
    this.sourceItems.update((items) => {
      items[0] = { ...items[0], name: items[0].name + '+' };
      return [...items]; // New array, but indexArray keeps stable signals
    });
  }

  // since the underlying source is a signal we can also create updaters in the mapper
  readonly updatableItems = indexArray(this.sourceItems, (child, index) => {

    return {
      value: computed(() => `Item ${index}: ${child().name}`))
      updateName: () => child.update((cur) => ({...cur, name: cur.name + '+'}))
    };
  });


  // since the underlying source is a WritableSignal we can also create updaters in the mapper
  readonly writableItems = indexArray(this.sourceItems, (child, index) => {

    return {
      value: computed(() => `Item ${index}: ${child().name}`))
      updateName: () => child.update((cur) => ({...cur, name: cur.name + '+'}))
    };
  });

  // if the source is a mutable signal we can even update them inline
  readonly sourceItems = mutable([
    { id: 1, name: 'A' },
    { id: 2, name: 'B' },
  ]);

  readonly mutableItems = indexArray(this.sourceItems, (child, index) => {

    return {
      value: computed(() => `Item ${index}: ${child().name}`))
      updateName: () => child.inline((cur) => {
        cur.name += '+';
      })
    };
  });
}
```

### mapObject

Projects a reactive object (Record<string, T>) into a new object (Record<string, U>), maintaining referential stability for values associated with unchanged keys. This is the Object-equivalent of keyArray.

The projection function receives the key and a value Signal. If the source is a WritableSignal or MutableSignal, the provided value signal is also writable (via derived), allowing child components or logic to update the specific property in the source object directly.

```ts
import { Component, signal, computed } from '@angular/core';
import { mapObject } from '@mmstack/primitives';

@Component({
  selector: 'app-settings',
  template: `
    @for (key of objectKeys(controls()); track key) {
      <div class="setting">
        <span>{{ controls()[key].label }}</span>
        <button (click)="controls()[key].toggle()">
          {{ controls()[key].isActive() ? 'ON' : 'OFF' }}
        </button>
      </div>
    }
  `,
})
export class SettingsComponent {
  objectKeys = Object.keys;

  // Source state
  readonly settings = signal<Record<string, boolean>>({
    wifi: true,
    bluetooth: false,
  });

  // Mapped object: { [key]: { label, isActive, toggle } }
  readonly controls = mapObject(
    this.settings,
    (key, value) => {
      // 'value' is a WritableSignal linked to this specific property
      return {
        label: key.toUpperCase(),
        isActive: value, // Expose as ReadOnly for template
        toggle: () => value.update((v) => !v),
        destroy: () => console.log(`Cleanup logic for ${key}`),
      };
    },
    {
      // Optional cleanup hook when a key is removed from the source
      onDestroy: (mappedItem) => mappedItem.destroy(),
    },
  );

  addSetting() {
    this.settings.update((s) => ({ ...s, airdrop: false }));
  }
}
```

### nestedEffect

Creates an effect that can be nested, similar to SolidJS's `createEffect`.

This primitive enables true hierarchical reactivity. A `nestedEffect` created within another `nestedEffect` is **automatically destroyed and recreated** when the parent re-runs.

It automatically handles injector propagation and lifetime management, allowing you to create fine-grained, conditional side-effects that only track dependencies when they are "live". This is a powerful optimization for scenarios where a "hot" signal (which changes often) should only be tracked when a "cold" signal (a condition that changes rarely) is true.

```ts
import { Component, signal } from '@angular/core';
import { nestedEffect } from '@mmstack/primitives';

@Component({ selector: 'app-nested-demo' })
export class NestedDemoComponent {
  // `coldGuard` changes rarely
  readonly coldGuard = signal(false);
  // `hotSignal` changes very often
  readonly hotSignal = signal(0);

  constructor() {
    // A standard effect would track *both* signals and run
    // every time `hotSignal` changes, even if `coldGuard` is false.
    // effect(() => {
    //   if (this.coldGuard()) {
    //     console.log('Hot signal is:', this.hotSignal());
    //   }
    // });

    // `nestedEffect` solves this:
    nestedEffect(() => {
      // This outer effect ONLY tracks `coldGuard`.
      // It does not track `hotSignal`.
      if (this.coldGuard()) {
        // This inner effect is CREATED when coldGuard is true
        // and DESTROYED when it becomes false.
        nestedEffect(() => {
          // It only tracks `hotSignal` while it exists.
          console.log('Hot signal is:', this.hotSignal());
        });
      }
    });
  }
}
```

#### Advanced Example: Fine-grained Lists

`nestedEffect` can be composed with `indexArray` to create truly fine-grained reactive lists, where each item can manage its own side-effects (like external library integrations) that are automatically cleaned up when the item is removed.

```ts
import { Component, signal, computed } from '@angular/core';
import { indexArray, nestedEffect } from '@mmstack/primitives';

@Component({ selector: 'app-list-demo' })
export class ListDemoComponent {
  readonly users = signal([
    { id: 1, name: 'Alice' },
    { id: 2, name: 'Bob' },
  ]);

  // indexArray creates stable signals for each item
  readonly mappedUsers = indexArray(
    this.users,
    (userSignal, index) => {
      // Create a side-effect tied to THIS item's lifetime
      const effectRef = nestedEffect(() => {
        // This only runs if `userSignal` (this specific user) changes.
        console.log(`User ${index} updated:`, userSignal().name);

        // e.g., updateAGGridRow(index, userSignal());
      });

      // Return the data and the cleanup logic
      return {
        label: computed(() => `User: ${userSignal().name}`),
        // This function will be called by `onDestroy`
        _destroy: () => effectRef.destroy(),
      };
    },
    {
      // When indexArray removes an item, it calls `onDestroy`
      onDestroy: (mappedItem) => {
        mappedItem._destroy(); // Manually destroy the nested effect
      },
    },
  );
}
```

### toWritable

A utility function that converts a read-only Signal into a WritableSignal by allowing you to provide custom implementations for the .set() and .update() methods. This is useful for creating controlled write access to signals that are naturally read-only (like those created by computed). This is used under the hood in derived.

```typescript
import { Component, signal, effect } from '@angular/core';
import { toWritable } from '@mmstack/primitives';

const user = signal({ name: 'John' });

const name = toWritable(
  computed(() => user().name),
  (name) => user.update((prev) => ({ ...prev, name })),
); // WritableSignal<string> bound to user signal
```

### derived

Creates a WritableSignal that represents a part of another source WritableSignal (e.g., an object property or an array element), enabling two-way data binding. Changes to the source update the derived signal, and changes to the derived signal (via .set() or .update()) update the source signal accordingly.

```typescript
const user = signal({ name: 'John' });

const name = derived(user, 'name'); // WritableSignal<string>, which updates user signal & reacts to changes in the name property

// Full syntax example
const name2 = derived(user, {
  from: (u) => u.name,
  onChange: (name) => user.update((prev) => ({ ...prev, name })),
});
```

### chunked

Creates a Signal that progressively emits segments of a source array, chunk by chunk. This is a time-slicing primitive designed to keep the main thread responsive when rendering large lists or processing heavy data sets.

Instead of rendering 10,000 items at once (which would freeze the UI), chunked emits the first batch immediately, then schedules the next batch to be added in the next frame (or after a delay), repeating until the full list is visible. If the source array changes, the process resets and starts over from the first chunk.

```ts
import { Component, signal } from '@angular/core';
import { chunked } from '@mmstack/primitives';

@Component({
  selector: 'app-heavy-list',
  template: `
    <div class="status-bar">Loaded: {{ visibleItems().length }} / {{ allItems().length }}</div>

    <ul>
      @for (item of visibleItems(); track item.id) {
        <li>{{ item.label }}</li>
      }
    </ul>
  `,
})
export class HeavyListComponent {
  // A heavy source with 10,000 items
  readonly allItems = signal(Array.from({ length: 10000 }, (_, i) => ({ id: i, label: `Item #${i}` })));

  // Process 100 items per animation frame to prevent UI blocking
  readonly visibleItems = chunked(this.allItems, {
    chunkSize: 100,
    delay: 'frame', // 'frame' | 'microtask' | number (ms)
  });
}
```

### tabSync

A low-level primitive that synchronizes a WritableSignal across multiple browser tabs or windows of the same application using the BroadcastChannel API. Used by the cache in @mmstack/resource & the stored signal.

When the signal is updated in one tab, the new value is broadcast and automatically set in the corresponding signal in all other open tabs. This is ideal for synchronizing global state like user sessions, theme preferences, or shopping cart data.

#### Key Features:

- SSR Safe: Gracefully degrades to a standard signal on the server.
- Automatic Cleanup: Handles event listeners and disconnects when the injection context is destroyed.
- Smart ID Generation: Can auto-generate IDs for rapid prototyping, but supports explicit IDs for production stability.

Note: While tabSync attempts to generate a deterministic ID based on the call site, it is highly recommended to provide a manual id string in production to ensure stability across different builds and minification processes.

```ts
import { Component, signal } from '@angular/core';
import { tabSync } from '@mmstack/primitives';

@Component({
  selector: 'app-sync-demo',
  template: `
    <p>Open this page in two tabs!</p>

    <button (click)="counter.update(n => n + 1)">Count: {{ counter() }}</button>

    <select [ngModel]="theme()" (ngModelChange)="theme.set($event)">
      <option value="light">Light</option>
      <option value="dark">Dark</option>
    </select>
  `,
})
export class SyncDemoComponent {
  // 1. Quick usage (Auto-ID)
  // Good for dev, but ID might change if code moves lines/files
  readonly counter = tabSync(signal(0));

  // 2. Production usage (Explicit ID)
  // Recommended: Ensures tabs always find each other regardless of minification
  readonly theme = tabSync(signal('light'), {
    id: 'global-app-theme',
  });
}
```

### withHistory

Enhances any WritableSignal with a complete undo/redo history stack. This is useful for building user-friendly editors, forms, or any feature where reverting changes is necessary. It provides .undo(), .redo(), and .clear() methods, along with reactive boolean signals like .canUndo and .canRedo to easily enable or disable UI controls.

```typescript
import { FormsModule } from '@angular/forms';
import { JsonPipe } from '@angular/common';
import { withHistory } from '@mmstack/primitives';
import { Component, signal, effect } from '@angular/core';

@Component({
  selector: 'app-history-demo',
  standalone: true,
  imports: [FormsModule, JsonPipe],
  template: `
    <h4>Simple Text Editor</h4>
    <textarea [(ngModel)]="text" rows="4" cols="50"></textarea>
    <div class="buttons" style="margin-top: 8px; display: flex; gap: 8px;">
      <button (click)="text.undo()" [disabled]="!text.canUndo()">Undo</button>
      <button (click)="text.redo()" [disabled]="!text.canRedo()">Redo</button>
      <button (click)="text.clear()" [disabled]="!text.canClear()">Clear History</button>
    </div>
    <p>History Stack:</p>
    <pre>{{ text.history() | json }}</pre>
  `,
})
export class HistoryDemoComponent {
  // Create a signal and immediately enhance it with history capabilities.
  text = withHistory(signal('Hello, type something!'), { maxSize: 10 });

  constructor() {
    // You can react to history changes as well
    effect(() => {
      console.log('History stack changed:', this.text.history());
    });
  }
}
```

### sensor

### sensor

The `sensor()` facade provides a unified way to create various reactive sensor signals that track browser events, states, and user preferences. You specify the type of sensor you want (e.g., `'mousePosition'`, `'networkStatus'`, `'windowSize'`, `'dark-mode'`), and it returns the corresponding signal, often with specific properties or methods. These primitives are generally SSR-safe and handle their own event listener cleanup.

You can either use the `sensor('sensorType', options)` facade or import the specific sensor functions directly if you prefer.

**Facade Usage Example:**

```typescript
import { sensor } from '@mmstack/primitives';
import { effect } from '@angular/core';

const network = sensor('networkStatus');
const mouse = sensor('mousePosition', { throttle: 50, coordinateSpace: 'page' });
const winSize = sensor('windowSize', { throttle: 150 });
const isDark = sensor('dark-mode');

effect(() => console.log('Online:', network().isOnline));
effect(() => console.log('Mouse X:', mouse().x));
effect(() => console.log('Window Width:', winSize().width));
effect(() => console.log('Dark Mode Preferred:', isDark()));
```

Individual sensors available through the facade or direct import:

#### mousePosition

Tracks the mouse cursor's position. By default, updates are throttled to 100ms. It provides the main throttled signal and an .unthrottled property to access the raw updates.

Key Options: target, coordinateSpace ('client' or 'page'), touch (boolean), throttle (ms).

```typescript
import { Component, effect } from '@angular/core';
import { sensor } from '@mmstack/primitives'; // Or import { mousePosition }
import { JsonPipe } from '@angular/common';

@Component({
  selector: 'app-mouse-tracker',
  standalone: true,
  imports: [JsonPipe],
  template: `
    <div (mousemove)="onMouseMove($event)" style="width: 300px; height: 200px; border: 1px solid black; padding: 10px; user-select: none;">Move mouse here...</div>
    <p><b>Throttled Position:</b> {{ mousePos() | json }}</p>
    <p><b>Unthrottled Position:</b> {{ mousePos.unthrottled() | json }}</p>
  `,
})
export class MouseTrackerComponent {
  // Using the facade
  readonly mousePos = sensor('mousePosition', { coordinateSpace: 'page', throttle: 200 });
  // Or direct import:
  // readonly mousePos = mousePosition({ coordinateSpace: 'page', throttle: 200 });

  // Note: The (mousemove) event here is just to show the example area works.
  // The mousePosition sensor binds its own listeners based on the target option.
  onMouseMove(event: MouseEvent) {
    // No need to call set, mousePosition handles it.
  }

  constructor() {
    effect(() => console.log('Throttled Mouse:', this.mousePos()));
    effect(() => console.log('Unthrottled Mouse:', this.mousePos.unthrottled()));
  }
}
```

#### networkStatus

Tracks the browser's online/offline status. The returned signal is a boolean (`true` for online) and has an attached `.since` signal indicating when the status last changed.

```typescript
import { Component, effect } from '@angular/core';
import { sensor } from '@mmstack/primitives'; // Or import { networkStatus }
import { DatePipe } from '@angular/common';

@Component({
  selector: 'app-network-info',
  standalone: true,
  imports: [DatePipe],
  template: `
    @if (netStatus()) {
      <p>✅ Online (Since: {{ netStatus.since() | date: 'short' }})</p>
    } @else {
      <p>❌ Offline (Since: {{ netStatus.since() | date: 'short' }})</p>
    }
  `,
})
export class NetworkInfoComponent {
  readonly netStatus = sensor('networkStatus');

  constructor() {
    effect(() => {
      console.log('Network online:', this.netStatus(), 'Since:', this.netStatus.since());
    });
  }
}
```

#### pageVisibility

Tracks the page's visibility state (e.g., 'visible', 'hidden') using the Page Visibility API.

```typescript
import { Component, effect } from '@angular/core';
import { sensor } from '@mmstack/primitives'; // Or import { pageVisibility }

@Component({
  selector: 'app-visibility-logger',
  standalone: true,
  template: `<p>Page is currently: {{ visibility() }}</p>`,
})
export class VisibilityLoggerComponent {
  readonly visibility = sensor('pageVisibility');

  constructor() {
    effect(() => {
      console.log('Page visibility changed to:', this.visibility());
      if (this.visibility() === 'hidden') {
        // Perform cleanup or pause tasks
      }
    });
  }
}
```

#### windowSize

Tracks the browser window's inner dimensions (width and height). Updates are throttled by default (100ms). It provides the main throttled signal and an .unthrottled property to access raw updates.

```typescript
import { Component, effect, computed } from '@angular/core';
import { sensor } from '@mmstack/primitives'; // Or import { windowSize }

@Component({
  selector: 'app-responsive-display',
  standalone: true,
  template: `
    <p>Current Window Size: {{ winSize().width }}px x {{ winSize().height }}px</p>
    <p>Unthrottled: W: {{ winSize.unthrottled().width }} H: {{ winSize.unthrottled().height }}</p>
    @if (isMobileDisplay()) {
      <p>Displaying mobile layout.</p>
    } @else {
      <p>Displaying desktop layout.</p>
    }
  `,
})
export class ResponsiveDisplayComponent {
  readonly winSize = sensor('windowSize', { throttle: 150 });
  // Or: readonly winSize = windowSize({ throttle: 150 });

  readonly isMobileDisplay = computed(() => this.winSize().width < 768);

  constructor() {
    effect(() => console.log('Window Size (Throttled):', this.winSize()));
  }
}
```

#### scrollPosition

Tracks the scroll position (x, y) of the window or a specified HTML element. Updates are throttled by default (100ms). It provides the main throttled signal and an .unthrottled property to access raw updates.

```typescript
import { Component, effect, ElementRef, viewChild } from '@angular/core';
import { sensor } from '@mmstack/primitives'; // Or import { scrollPosition }
import { JsonPipe } from '@angular/common';

@Component({
  selector: 'app-scroll-indicator',
  standalone: true,
  imports: [JsonPipe],
  template: `
    <div style="height: 100px; border-bottom: 2px solid red; position: fixed; top: 0; left: 0; width: 100%; background: white; z-index: 10;">
      Page Scroll Y: {{ pageScroll().y }}px
      <p>Unthrottled Y: {{ pageScroll.unthrottled().y }}</p>
    </div>
    <div #scrollableContent style="height: 2000px; padding-top: 120px;">Scroll down...</div>
  `,
})
export class ScrollIndicatorComponent {
  readonly pageScroll = sensor('scrollPosition', { throttle: 50 });
  // Or: readonly pageScroll = scrollPosition({ throttle: 50 });

  constructor() {
    effect(() => {
      // Example: Change header style based on scroll
      console.log('Page scroll Y (Throttled):', this.pageScroll().y);
    });
  }
}
```

#### mediaQuery, prefersDarkMode() & prefersReducedMotion()

A generic mediaQuery primitive, you can use directly for any CSS media query. Two specific versions have been created for `prefersDarkMode()` & `prefersReducedMotion()`.
Reacts to changes in preferences & exposes a `Signal<boolean>`.

```typescript
import { Component, effect } from '@angular/core';
import { mediaQuery, prefersDarkMode, prefersReducedMotion } from '@mmstack/primitives'; // Direct import

@Component({
  selector: 'app-layout-checker',
  standalone: true,
  template: `
    @if (isLargeScreen()) {
      <p>Using large screen layout.</p>
    } @else {
      <p>Using small screen layout.</p>
    }
  `,
})
export class LayoutCheckerComponent {
  readonly isLargeScreen = mediaQuery('(min-width: 1280px)');
  readonly prefersDark = prefersDarkMode(); // is just a pre-defined mediaQuery signal
  readonly prefersReducedMotion = prefersReducedMotion(); // is just a pre-defined mediaQuery signal
  constructor() {
    effect(() => {
      console.log('Is large screen:', this.isLargeScreen());
    });
  }
}
```

### until

The `until` primitive provides a powerful way to bridge Angular's reactive signals with imperative, Promise-based asynchronous code. It returns a Promise that resolves when the value of a given signal satisfies a specified predicate function.

This is particularly useful for:

- Orchestrating complex sequences of operations (e.g., waiting for data to load or for a user action to complete before proceeding).
- Writing tests where you need to await a certain state before making assertions.
- Integrating with other Promise-based APIs.

It also supports optional timeouts and automatic cancellation via DestroyRef if the consuming context (like a component) is destroyed before the condition is met.

```typescript
import { signal } from '@angular/core';
import { until } from '@mmstack/primitives';

it('should reject on timeout if the condition is not met in time', async () => {
  const count = signal(0);
  const timeoutDuration = 500;

  const untilPromise = until(count, (value) => value >= 10, { timeout: timeoutDuration });

  // Simulate a change that doesn't meet the condition
  setTimeout(() => count.set(1), 10);

  await expect(untilPromise).toThrow(`until: Timeout after ${timeoutDuration}ms.`);
});
```

### elementVisibility

Tracks if a target DOM element is intersecting with the viewport (or a specified root element) using the `IntersectionObserver` API. This is highly performant for use cases like lazy-loading content or triggering animations when elements scroll into view.

It can observe a static `ElementRef`/`Element` or a `Signal` that resolves to one, allowing for dynamic targets. The returned signal emits the full `IntersectionObserverEntry` object (or `undefined`) & exposes a sub-signal `.visible` which is just a boolean signal for ease of use

```typescript
import { Component, effect, ElementRef, viewChild, computed } from '@angular/core';
import { elementVisibility } from '@mmstack/primitives';

@Component({
  selector: 'app-lazy-load-item',
  standalone: true,
  template: `
    <div #itemToObserve style="height: 300px; margin-top: 100vh; border: 2px solid green;">
      @if (intersectionEntry.visible()) {
        <p>This content was lazy-loaded because it became visible!</p>
      } @else {
        <p>Item is off-screen. Scroll down to load it.</p>
      }
    </div>
  `,
})
export class LazyLoadItemComponent {
  readonly itemRef = viewChild.required<ElementRef<HTMLDivElement>>('itemToObserve', {
    read: ElementRef,
  });

  // Observe the element, get the full IntersectionObserverEntry
  readonly intersectionEntry = elementVisibility(this.itemRef);

  constructor() {
    effect(() => {
      if (this.intersectionEntry.visible()) {
        console.log('Item is now visible!', this.intersectionEntry());
      } else {
        console.log('Item is no longer visible or not yet visible.');
      }
    });
  }
}
```