JavaScript - Starting with the basics - Strings(String traversal with a for loop, length, substr, charCodeAt, fomCharCode) - Think JavaScript(?)

Think Perl 6

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)

Think Perl 6: How to Think Like a Computer Scientist (Laurent Rosenfeld(著)、Allen B. Downey(著)、Oreilly & Associates Inc)のPart 1(Starting with the basics)、Chapter 7(Strings)の Boolean functions の String traversal with a for loop の Exercise.を JavaScript で取り組 んでみる。

String traversal with a for loop の Exercise.

コード(Emacs)

HTML5

letters: <input id="letters0" type="text" value="banana">
<button id="run0">run</button>
<button id="clear0">clear</button>
<pre id="output0"></pre>

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

JavaScript

let input0 = document.querySelector('#letters0'),
    btn0 = document.querySelector('#run0'),
    btn1 = document.querySelector('#clear0'),
    pre0 = document.querySelector('#output0');

let backward = (letters) => {
    let index = letters.length;

    while (index > 0) {
        index -= 1;
        let letter = letters.substr(index, 1);
        pre0.textContent += `${letter}\n`;
    }
};

let output = () => {
    pre0.textContent += '1.\n';
    let letters = input0.value;

    backward(letters);

    pre0.textContent += '2.\n';
    let suffix = 'ack',
        jCode = 'J'.charCodeAt(0),
        qCode = 'Q'.charCodeAt(0);

    for (let code = jCode; code <= qCode; code += 1) {
        let letter = String.fromCharCode(code);

        if (letter === 'O' || letter === 'Q') {
            pre0.textContent += `${letter}u${suffix}\n`
        } else {
            pre0.textContent += `${letter}${suffix}\n`
        }
    }
};
    

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

output();

letters: