generator.js

const wait = function*(bullet, n) {
    for(let i = 0; i < n; ++i) {
        bullet = yield {
            isChangeScript: false,
            changedBullet: bullet,
            newBullets: [],
        };
    }

    return bullet;
};

const script = function*(bullet) {
    while (true) {
        bullet = yield* wait(bullet, 1);
        bullet = yield {
            isChangeScript: false,
            changedBullet: {
                x: bullet.x,
                y: bullet.y,
                angle: bullet.angle + 1,
                script,
                scriptGenerator: null,
            },
            newBullets: [
                {
                    x: 0,
                    y: 0,
                    angle: 0,
                    script,
                    scriptGenerator: null,
                },
            ],
        };
    }
};

runScript = bullet => {
    const scriptGenerator = bullet.scriptGenerator === null ? bullet.script(bullet) : bullet.scriptGenerator;
    const { done, value } = scriptGenerator.next(bullet);

    if (value === undefined) {
        return [];
    }

    const { isChangeScript, changedBullet, newBullets } = value;

    return [
        {
            x: changedBullet.x,
            y: changedBullet.y,
            angle: changedBullet.angle,
            script: changedBullet.script,
            scriptGenerator: isChangeScript ? null : scriptGenerator,
        },
        ...newBullets,
    ];
}

let bullets = [
    {
        x: 0,
        y: 0,
        angle: 0,
        script,
        scriptGenerator: null,
    },
];

bullets = bullets.map(runScript).reduce((accumulated, bullet) => [...accumulated, ...bullet], []);
console.log(bullets);
console.log('');
bullets = bullets.map(runScript).reduce((accumulated, bullet) => [...accumulated, ...bullet], []);
console.log(bullets);
console.log('');
bullets = bullets.map(runScript).reduce((accumulated, bullet) => [...accumulated, ...bullet], []);
console.log(bullets);
console.log('');