JavaScript - Function Decorators: Wrapping Functions(Creating a Function Decorator, nested function) - Head First JavaScript(?)

Head First Python

開発環境

• macOS Sierra - Apple (OS)
• Emacs (Text Editor)
• JavaScript (プログラミング言語)
• Node.js, Safari(JavaScript エンジン)
• Learning JavaScript [邦訳] (参考書籍)

Head First Python (Paul Barry (著)、O'Reilly Media)のChapter 10.(Function Decorators: Wrapping Functions) の SHARPEN YOUR PENCIL(No. 7523) を JavaScript で取り組んでみる。

Relational Database は MySQL、MariaDBの代わりに IndexedDB(とDexie.js、JavaScript library) を使用。(大雑把なイメージだけ。)

SHARPEN YOUR PENCIL(No. 6522)

コード(Emacs)

HTML5

<button id="run0">run</button>
<button id="clear0">clear</button>
<pre id="output0"></pre>

<script src="sample4.js"></script>

JavaScript

let btn0 = document.querySelector('#run0'),
    btn1 = document.querySelector('#clear0'),
    pre0 = document.querySelector('#output0'),
    session = {};

let checkLoggedIn = (fn) => {
    return () => {
        if (session['logged_in']) {
            return fn();
        }
        return 'You are NOT logged in';
    };
};

let test = checkLoggedIn(
    () => {
        return 'logged in';
    }
);

let output = () => {
    pre0.textContent += test() + '\n';
    session['logged_in'] = true;
    pre0.textContent += test() + '\n';
    delete session['logged_in'];
    pre0.textContent += test() + '\n';
};

btn0.onclick = output;
btn1.onclick = () => {
    pre0.textContent = '';
};

output();