> For the complete documentation index, see [llms.txt](https://www.learnrxjs.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.learnrxjs.io/learn-rxjs/recipes/tank-battle-game.md).
# Tank Battle Game
*By* [*adamlubek*](https://github.com/adamlubek)
This recipe demonstrates RxJS implementation of Tank Battle like game.
### Example Code
( [StackBlitz](https://stackblitz.com/edit/rxjs-tank-battle?file=index.ts) )
#### index.ts
```js
// RxJS v6+
import { fromEvent, combineLatest, interval } from 'rxjs';
import { scan, tap, startWith } from 'rxjs/operators';
import { gameSize, down, up, right, left, p1Color, p2Color } from './constants';
import { State } from './interfaces';
import {
updatePlayer,
addShots,
updateShots,
checkCollisions,
initialState
} from './game';
import { paint } from './html-renderer';
combineLatest(
interval(100),
fromEvent(document, 'keydown').pipe(startWith({ key: '' }))
)
.pipe(
scan < [number, KeyboardEvent],
State >
((state, [_, event]) => (
updatePlayer(state.players[0], event.key, 'w', 's', 'a', 'd'),
updatePlayer(state.players[1], event.key, 'i', 'k', 'j', 'l'),
addShots(state, event.key),
(state.shots = updateShots(state.shots)),
checkCollisions(state),
state
),
initialState),
tap(paint)
)
.subscribe();
```
#### game.ts
```js
import {
gameSize,
down,
up,
right,
left,
p1Color,
p2Color,
p1Shot,
p2Shot
} from './constants';
import { GameObject, State } from './interfaces';
const gameObject = (x, y, g, c): GameObject => ({ x, y, g, s: 0, c: c });
const noop = (): void => {};
export const updatePlayer = (
p: GameObject,
key: string,
u,
d,
l,
r
): GameObject => (
key === d
? ((p.x += p.x < gameSize - 1 ? 1 : 0), (p.g = down))
: key === u
? ((p.x += p.x > 0 ? -1 : 0), (p.g = up))
: noop,
key === r
? ((p.y += p.y < gameSize - 1 ? 1 : 0), (p.g = right))
: key === l
? ((p.y += p.y > 0 ? -1 : 0), (p.g = left))
: noop,
p
);
export const addShot = (player: GameObject): GameObject => ({
x: player.x,
y: player.y,
g: player.g
});
export const addShots = (state: State, key: string): void =>
state.shots.push(
key === p1Shot
? addShot(state.players[0])
: key === p2Shot
? addShot(state.players[1])
: []
);
export const updateShots = (shots: GameObject[]): GameObject[] =>
shots
.filter(s => s.x > 0 && s.x < gameSize - 1 && s.y > 0 && s.y < gameSize)
.map(
s => (
s.g === down
? (s.x += 1)
: s.g === up
? (s.x += -1)
: s.g === right
? (s.y += 1)
: s.g === left
? (s.y += -1)
: () => {},
s
)
);
export const initialState: State = {
players: [
gameObject(1, 1, right, p1Color),
gameObject(gameSize - 2, gameSize - 2, left, p2Color)
],
shots: []
};
export const checkCollisions = (state: State): void =>
state.players.forEach((p, i) => {
const collidingShotIndex = state.shots.findIndex(
s => s.x === p.x && s.y === p.y
);
if (collidingShotIndex > -1) {
if (i === 0) {
state.players[1].s += 1;
} else {
state.players[0].s += 1;
}
state.shots.splice(collidingShotIndex, 1);
}
});
```
#### interfaces.ts
```js
export interface GameObject {
x: number;
y: number;
g: string;
s: number;
c: string;
}
export interface State {
players: GameObject[];
shots: GameObject[];
}
```
#### constants.ts
```js
export const gameSize = 20;
export const up = '^';
export const down = 'v';
export const left = '<';
export const right = '>';
export const empty = 0;
export const p1Color = 'DarkViolet';
export const p2Color = 'CornflowerBlue';
export const p1Shot = 'c';
export const p2Shot = 'n';
```
#### html-renderer.ts
```js
import { gameSize, empty, p1Color, p2Color } from './constants';
import { State, GameObject } from './interfaces';
const createElem = (gameObject: GameObject) => {
const elem = document.createElement('div');
elem.style.display = 'inline-block';
elem.style.marginLeft = '10px';
elem.style.height = '6px';
elem.style.width = '6px';
elem.style.color = gameObject.c;
elem.innerText = gameObject === empty ? ' ' : gameObject.g;
return elem;
};
const paintPlayerScore = (score: number, color: string) => {
const scoreElem = document.createElement('span');
scoreElem.innerHTML = `P1: ${score} `;
scoreElem.style.color = color;
document.body.appendChild(scoreElem);
};
const paintScores = (state: State) => {
document.body.innerHTML = 'Scores: ';
paintPlayerScore(state.players[0].s, p1Color);
paintPlayerScore(state.players[1].s, p2Color);
};
const painInfo = () => {
document.body.innerHTML += 'This game requires 2 players :)';
document.body.innerHTML += '
';
document.body.innerHTML += 'Player 1 controls: wsad, fire: c';
document.body.innerHTML += '
';
document.body.innerHTML += 'Player 2 controls: ikjl, fire: n';
};
const emptyGame = () =>
Array(gameSize)
.fill(empty)
.map(_ => Array(gameSize).fill(empty));
const paintGame = (state: State) => {
const game = emptyGame();
state.players.forEach(p => (game[p.x][p.y] = { g: p.g, c: p.c }));
state.shots.forEach(s => (game[s.x][s.y] = { g: '*', c: 'black' }));
game.forEach(row => {
const rowContainer = document.createElement('div');
row.forEach(col => rowContainer.appendChild(createElem(col)));
document.body.appendChild(rowContainer);
});
};
export const paint = (state: State) => {
paintScores(state);
document.body.innerHTML += '
';
paintGame(state);
painInfo();
};
```
### Operators Used
* [combineLatest](/learn-rxjs/operators/combination/combinelatest.md)
* [fromEvent](/learn-rxjs/operators/creation/fromevent.md)
* [interval](/learn-rxjs/operators/creation/interval.md)
* [scan](/learn-rxjs/operators/transformation/scan.md)
* [startWith](/learn-rxjs/operators/combination/startwith.md)
* [tap](/learn-rxjs/operators/utility/do.md)
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