JavaScript - Calculations(Currency Conversion)

Exercises for Programmers

開発環境

• OS X El Capitan - Apple (OS)
• Emacs (Text Editor)
• JavaScript (プログラミング言語)
• jQuery (Library)
• Safari(Web browser)

Exercises for Programmers: 57 Challenges to Develop Your Coding Skills (Brian P. Hogan 著、Pragmatic Bookshelf)のChapter 3(Calculations)、11(Currency Conversion)を取り組んでみる。

11(Currency Conversion)

コード(Emacs)

<label for="amount_from">
  How many euros are you exchanging? 
</label>
<input id="amount_from" type="number" min="1" step="1" value="81">
<br>
<label for="rate_from">
  What is the exchange rate?
</label>
<input id="rate_from" type="number" min="0" step="0.01" value="137.51">
<br>
<span class="amount_from"></span> euros at an exchange rate of
<span class="rate_from"></span> is <span class="amount_to"></span> U.S.
dollars.

<script src="sample11.js"></script>

(function (){
    var amount_from,
        rate_from,

        input_amount_from = document.querySelector('#amount_from'),
        input_rate_from = document.querySelector('#rate_from'),
        inputs = [input_amount_from, input_rate_from],
        class_amount_from = document.querySelectorAll('.amount_from'),
        class_rate_from = document.querySelectorAll('.rate_from'),
        class_amount_to = document.querySelectorAll('.amount_to'),
        
        calc,
        display;

    calc = function () {
        var rate_to = 100,
            amount_to;
        
        amount_from = parseFloat(input_amount_from.value);
        rate_from = parseFloat(input_rate_from.value);
        amount_to = Math.floor(amount_from * rate_from / rate_to * 100) / 100;

        return amount_to;
    };

    display = function () {
        var i,
            max,
            amount_to = calc();

        for (i = 0, max = class_amount_from.length; i < max; i += 1) {
            class_amount_from[i].innerHTML = amount_from;
        }
        for (i = 0, max = class_rate_from.length; i < max; i += 1) {
            class_rate_from[i].innerHTML = rate_from;
        }
        for (i = 0, max = class_amount_to.length; i < max; i += 1) {
            class_amount_to[i].innerHTML = amount_to;
        }
    };

    inputs.forEach(function (input) {
        input.onchange = display;
        input.onkeyup = display;
    });
    
    display();
}());

How many euros are you exchanging?
What is the exchange rate?
euros at an exchange rate of is U.S. dollars.