Leveraging RXJS for real-time response to keyboard and mouse click combinations in web

Question

Leveraging RXJS for real-time response to keyboard and mouse click combinations in web

I am new to RXJS and looking for a way to drag an HtmlElement when the user presses the space key and then drags the element with the mouse.

The dragging should be initiated by either pressing the SPACE key followed by a left click, or vice versa. The dragging will end when the SPACE key is released (keyup event) or when the mouse button is clicked (mouseup event), whichever happens first.

To implement this, I have created four observables for the specific events:

spaceDown$ = fromEvent<KeyboardEvent>(document, "keydown").pipe( filter(key => key.code === 'Space'))

spaceUp$ = fromEvent<KeyboardEvent>(document, "keyup").pipe( filter( key => key.code === 'Space'))

mouseDown$ = fromEvent<MouseEvent>(document, "mousedown").pipe( filter( mouse => mouse.button == 0))

mouseUp$ = fromEvent<MouseEvent>(document, "mouseup").pipe( filter( mouse => mouse.button == 0))

I have tried using operators like 'combineLatest', 'withLatestFrom', 'merge' on these streams but have not been able to achieve the desired behavior yet. Any suggestions on how to accomplish this?

angular typescript rxjs mouseevent keyboard-events

Answer 1

Answer №1

To handle drag events, I suggest mapping the source observables to a boolean value, where true represents pressed. Create combined observables for both keyboard and mouse inputs, then merge those two streams. When both values are true, it indicates a drag start event; otherwise, it's a drag end event.

const spaceDown$ = fromEvent<KeyboardEvent>(document, 'keydown').pipe(
  filter((key) => key.code === 'Space'),
  map(() => true)
);

const spaceUp$ = fromEvent<KeyboardEvent>(document, 'keyup').pipe(
  filter((key) => key.code === 'Space'),
  map(() => false)
);

const mouseDown$ = fromEvent<MouseEvent>(document, 'mousedown').pipe(
  filter((mouse) => mouse.button == 0),
  map(() => true)
);

const mouseUp$ = fromEvent<MouseEvent>(document, 'mouseup').pipe(
  filter((mouse) => mouse.button == 0),
  map(() => false)
);

const key$ = merge(spaceDown$, spaceUp$).pipe(startWith(false));
const mouse$ = merge(mouseDown$, mouseUp$).pipe(startWith(false));

const combined$ = combineLatest([
  key$,
  mouse$,
]).pipe(
  map(([key, mouse]) => key && mouse),
  distinctUntilChanged(),
);

combined$.subscribe((res) => console.log('combined$', res));

// Separate streams for dragstart and dragend:

const [dragStart$, dragEnd$] = partition(combined$, (val) => val);

dragStart$.subscribe(() => console.log('dragStart$'));
dragEnd$.subscribe(() => console.log('dragEnd$'));

Answer 2

To handle drag events, I suggest mapping the source observables to a boolean value, where true represents pressed. Create combined observables for both keyboard and mouse inputs, then merge those two streams. When both values are true, it indicates a drag start event; otherwise, it's a drag end event.

const spaceDown$ = fromEvent<KeyboardEvent>(document, 'keydown').pipe(
  filter((key) => key.code === 'Space'),
  map(() => true)
);

const spaceUp$ = fromEvent<KeyboardEvent>(document, 'keyup').pipe(
  filter((key) => key.code === 'Space'),
  map(() => false)
);

const mouseDown$ = fromEvent<MouseEvent>(document, 'mousedown').pipe(
  filter((mouse) => mouse.button == 0),
  map(() => true)
);

const mouseUp$ = fromEvent<MouseEvent>(document, 'mouseup').pipe(
  filter((mouse) => mouse.button == 0),
  map(() => false)
);

const key$ = merge(spaceDown$, spaceUp$).pipe(startWith(false));
const mouse$ = merge(mouseDown$, mouseUp$).pipe(startWith(false));

const combined$ = combineLatest([
  key$,
  mouse$,
]).pipe(
  map(([key, mouse]) => key && mouse),
  distinctUntilChanged(),
);

combined$.subscribe((res) => console.log('combined$', res));

// Separate streams for dragstart and dragend:

const [dragStart$, dragEnd$] = partition(combined$, (val) => val);

dragStart$.subscribe(() => console.log('dragStart$'));
dragEnd$.subscribe(() => console.log('dragEnd$'));

Answer 3

Answer №2

There are multiple approaches to achieving this, and here are two options:

Option 1: The "dummy" approach

In this solution, behavior subjects are used to control movement by filtering when to listen.

If you are not familiar with operators, this approach is easy to understand and works effectively.

import {
  BehaviorSubject,
  combineLatest,
  filter,
  fromEvent,
  map,
  Observable,
  switchMap,
  throttleTime,
} from 'rxjs';

// Code implementation omitted for brevity

moving$.pipe(throttleTime(100)).subscribe(() => console.log('dragging'));

Option 2: The "advanced" approach

This option may be more challenging to comprehend but aligns with your requirements.

The process involves creating a "starting" listener using `combineLatest` and a "stopping" condition using `race` operator.

Unlike combineLatest, race emits when any of its members emit, and the behavior repeats accordingly.

Finally, the behavior switches to the desired observable (mouse moving) until the stopping condition is met, repeating the process as needed.

import {
  combineLatest,
  filter,
  first,
  fromEvent,
  Observable,
  race,
  repeat,
  switchMap,
  takeUntil,
  throttleTime,
} from 'rxjs';

// Code implementation omitted for brevity

moving$.pipe(throttleTime(100)).subscribe(() => console.log('dragging'));

Answer 4

There are multiple approaches to achieving this, and here are two options:

Option 1: The "dummy" approach

In this solution, behavior subjects are used to control movement by filtering when to listen.

If you are not familiar with operators, this approach is easy to understand and works effectively.

import {
  BehaviorSubject,
  combineLatest,
  filter,
  fromEvent,
  map,
  Observable,
  switchMap,
  throttleTime,
} from 'rxjs';

// Code implementation omitted for brevity

moving$.pipe(throttleTime(100)).subscribe(() => console.log('dragging'));

Option 2: The "advanced" approach

This option may be more challenging to comprehend but aligns with your requirements.

The process involves creating a "starting" listener using `combineLatest` and a "stopping" condition using `race` operator.

Unlike combineLatest, race emits when any of its members emit, and the behavior repeats accordingly.

Finally, the behavior switches to the desired observable (mouse moving) until the stopping condition is met, repeating the process as needed.

import {
  combineLatest,
  filter,
  first,
  fromEvent,
  Observable,
  race,
  repeat,
  switchMap,
  takeUntil,
  throttleTime,
} from 'rxjs';

// Code implementation omitted for brevity

moving$.pipe(throttleTime(100)).subscribe(() => console.log('dragging'));

Leveraging RXJS for real-time response to keyboard and mouse click combinations in web

Answer №1

Answer №2

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