JavaScript - Extra strength objects - Using Prototypes(dynamic)

Head First JavaScript Programming

開発環境

• macOS Sierra - Apple (OS)
• Emacs (Text Editor)
• JavaScript (プログラミング言語)
• Safari(Web browser)

Head First JavaScript Programming (Eric T. Freeman (著)、Elisabeth Robson (著)、O'Reilly Media)の Chapter 13.(Extra strength objects - Using Prototypes)の EXERCISE(No. 8473)を取り組んでみる。

EXERCISE(No. 8473)

コード(Emacs)

HTML5

<pre id="output0"></pre>
<button id="run0">run</button>
<button id="clear0">clear</button>
<script src="sample4.js"></script>

JavaScript

let btn0 = document.querySelector('#run0'),
    btn1 = document.querySelector('#clear0'),
    pre0 = document.querySelector('#output0'),
    p = (x) => pre0.textContent += x + '\n',
    range = (start, end, step=1) => {
        let result = [];
        for (let i = start; i < end; i += 1) {
            result.push(i);
        }
        return result;
    };

let Game = () => {
    let that = {},
        level = 0,
        unlocked = false;
        play = () => {
            level += 1;
            p(`Welcome to level ${level}`);
            unlock();
        },
        unlock = () => {
            if (level === 42) {
                unlocked = true;
            }
        };    
    
    that.play = play;
    that.getLevel = () => level;
    that.getUnlocked = () => unlocked;

    return that;
};

let Robot = (name, year, owned, game) => {
    let that = {},
        deployLaser = () => {
            if (game.getUnlocked()) {
                p(`${name} is blasting you with laser beams.`);
            }
        },
        toString = () =>
        `${name} was made by ObjectsRUs in ${year} and is owned by ${owned}`;

    that.toString = toString;
    that.deployLaser = deployLaser;
    
    return that;
};

let output = () => {
    let game = Game(),
        robby = Robot('Robby', 1956, 'Dr.Morbius', game),
        rosie = Robot('Rosie', 1962, 'George Jetson', game);

    for (;game.getLevel() < 42;) {
        robby.deployLaser();
        rosie.deployLaser();
        game.play();
    }
    
    robby.deployLaser();
    rosie.deployLaser();
};

let clear = () => pre0.textContent = '';

btn0.onclick = output;
btn1.onclick = clear;

output();