JavaScript - Calculations(Computing Simple Interest)

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)、12(Computing Simple Interest)を取り組んでみる。

12(Computing Simple Interest)

コード(Emacs)

<label for="principal">
  Etner the principal:
</label> 
<input id="principal" type="number" min="0" step=".01" value="1500">
<br>
<label for="rate">
  Enter the rate of interest: 
</label>
<input id="rate" type="number" min="0" step="0.01" value="4.3">
<br>
<label for="years">
  Enter the number of years: 
</label>
<input id="years" type="number" min="0" step="1" value="4">
<br>
<p>
  After <span class="years"></span> years at <span class="rate"></span>% the
  investment will be worth $<span class="amount"></span>.
</p>

<script src="sample12.js"></script>

(function () {
    'use strict';
    var input_principal = document.querySelector('#principal'),
        input_rate = document.querySelector('#rate'),
        input_years = document.querySelector('#years'),
        inputs = [input_principal, input_rate, input_years],

        span_years = document.querySelectorAll('.years'),
        span_rate = document.querySelectorAll('.rate'),
        span_amount = document.querySelectorAll('.amount'),
        
        calc,
        display;

    calc = function (principal, rate, years) {
        return Math.round((principal * (1 + rate * years)) * 100) / 100;
    };

    display = function () {
        var amount,
            principal = parseFloat(input_principal.value),
            rate = parseFloat(input_rate.value),
            years = parseInt(input_years.value, 10),
            i,
            max;

        amount = calc(principal, rate / 100, years);

        for (i = 0, max = span_years.length; i < max; i += 1) {
            span_years[i].innerText = years;
        }
        for (i = 0, max = span_rate.length; i < max; i += 1) {
            span_rate[i].innerText = rate;
        }
        for (i = 0, max = span_amount.length; i < max; i += 1) {
            span_amount[i].innerText = amount;
        }
    };

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

    display();
}());

Etner the principal:
Enter the rate of interest:
Enter the number of years:

After years at % the investment will be worth $.