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Alphabet Invasion Game
This recipe demonstrates RxJS implementation of Alphabet Invasion Game.
Example Code
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Alphabet Invasion
index.ts
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// RxJS v6+
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import { interval, fromEvent, combineLatest, BehaviorSubject } from 'rxjs';
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import { scan, startWith, map, takeWhile, switchMap } from 'rxjs/operators';
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import { State, Letter, Letters } from './interfaces';
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​
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const randomLetter = () =>
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String.fromCharCode(
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Math.random() * ('z'.charCodeAt(0) - 'a'.charCodeAt(0)) + 'a'.charCodeAt(0)
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);
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const levelChangeThreshold = 20;
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const speedAdjust = 50;
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const endThreshold = 15;
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const gameWidth = 30;
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​
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const intervalSubject = new BehaviorSubject(600);
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​
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const letters$ = intervalSubject.pipe(
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switchMap(i =>
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interval(i).pipe(
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scan<number, Letters>
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(letters => ({
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intrvl: i,
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ltrs: [
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{
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letter: randomLetter(),
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yPos: Math.floor(Math.random() * gameWidth)
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},
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...letters.ltrs
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]
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}),
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{ ltrs: [], intrvl: 0 })
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)
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)
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);
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​
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const keys$ = fromEvent(document, 'keydown').pipe(
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startWith({ key: '' }),
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map((e: KeyboardEvent) => e.key)
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);
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​
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const renderGame = (state: State) => (
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(document.body.innerHTML = `Score: ${state.score}, Level: ${state.level} <br/>`),
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state.letters.forEach(
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l =>
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(document.body.innerHTML += ' '.repeat(l.yPos) + l.letter + '<br/>')
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),
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(document.body.innerHTML +=
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'<br/>'.repeat(endThreshold - state.letters.length - 1) +
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'-'.repeat(gameWidth))
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);
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const renderGameOver = () => (document.body.innerHTML += '<br/>GAME OVER!');
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const noop = () => {};
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​
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const game$ = combineLatest(keys$, letters$).pipe(
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scan<[string, Letters], State>
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((state, [key, letters]) => (
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letters.ltrs[letters.ltrs.length - 1] &&
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letters.ltrs[letters.ltrs.length - 1].letter === key
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? ((state.score = state.score + 1), letters.ltrs.pop())
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: noop,
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state.score > 0 && state.score % levelChangeThreshold === 0
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? ((letters.ltrs = []),
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(state.level = state.level + 1),
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(state.score = state.score + 1),
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intervalSubject.next(letters.intrvl - speedAdjust))
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: noop,
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{ score: state.score, letters: letters.ltrs, level: state.level }
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),
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{ score: 0, letters: [], level: 1 }),
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takeWhile(state => state.letters.length < endThreshold)
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);
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​
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game$.subscribe(renderGame, noop, renderGameOver);
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interfaces.ts
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export interface Letter {
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letter: String;
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yPos: number;
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}
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export interface Letters {
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ltrs: Letter[];
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intrvl: number;
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}
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export interface State {
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score: number;
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letters: Letter[];
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level: number;
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}
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Operators Used
Last modified 7mo ago
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