---
# System prepended metadata

title: '小專案五: DOM Array Methods | Array的應用'
tags: [JS小專案]

---

# 小專案五: DOM Array Methods | Array的應用
###### tags: `JS小專案`

## 成品示意圖
![](https://i.imgur.com/6nfQgyF.png)

## HTML的結構

首先是基礎的連結，將現有的圖片、CSS檔案和JavaScript檔案連結起來

```htmlembedded=
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" href="style.css"></link>
  <title>Exchange Rate Calculator</title>
</head>
<body>
  <img src="img/money.png" alt="" class="money-img">
  <h1>Exchange Rate Calculator</h1>
  <p>Choose the currency and the amounts to get the exchange rate</p>
```

接著是匯率轉換器下拉式選單需要使用的各類匯率，由於轉換器有input和output兩個部分，所以需要製作兩個class為currency的列表，選單id命名為currency-one與currency-two，中間再設計一個可切換的按鈕，並且嚴格限制輸入資料為數字(number)，並且分別制定id，以利後續js的撰寫

```htmlembedded=
  <div class= "container"></div>
    <div class = "currency">
      <select id="currency-one">
        <option value="AED">AED</option>
          <option value="ARS">ARS</option>
          <option value="AUD">AUD</option>
          <option value="BGN">BGN</option>
          <option value="BRL">BRL</option>
          <option value="BSD">BSD</option>
          <option value="CAD">CAD</option>
          <option value="CHF">CHF</option>
          <option value="CLP">CLP</option>
          <option value="CNY">CNY</option>
          <option value="COP">COP</option>
          <option value="CZK">CZK</option>
          <option value="DKK">DKK</option>
          <option value="DOP">DOP</option>
          <option value="EGP">EGP</option>
          <option value="EUR">EUR</option>
          <option value="FJD">FJD</option>
          <option value="GBP">GBP</option>
          <option value="GTQ">GTQ</option>
          <option value="HKD">HKD</option>
          <option value="HRK">HRK</option>
          <option value="HUF">HUF</option>
          <option value="IDR">IDR</option>
          <option value="ILS">ILS</option>
          <option value="INR">INR</option>
          <option value="ISK">ISK</option>
          <option value="JPY">JPY</option>
          <option value="KRW">KRW</option>
          <option value="KZT">KZT</option>
          <option value="MXN">MXN</option>
          <option value="MYR">MYR</option>
          <option value="NOK">NOK</option>
          <option value="NZD">NZD</option>
          <option value="PAB">PAB</option>
          <option value="PEN">PEN</option>
          <option value="PHP">PHP</option>
          <option value="PKR">PKR</option>
          <option value="PLN">PLN</option>
          <option value="PYG">PYG</option>
          <option value="RON">RON</option>
          <option value="RUB">RUB</option>
          <option value="SAR">SAR</option>
          <option value="SEK">SEK</option>
          <option value="SGD">SGD</option>
          <option value="THB">THB</option>
          <option value="TRY">TRY</option>
          <option value="TWD">TWD</option>
          <option value="UAH">UAH</option>
          <option value="USD" selected>USD</option>
          <option value="UYU">UYU</option>
          <option value="VND">VND</option>
          <option value="ZAR">ZAR</option>
      </select>
      <input type ="number" id="amount-one" placeholder="0" value="1">
    </div>

    
  <div class="swap-rate-container">
    <button class="btn" id="swap">
      
      Swap
    </button>
    <div class="rate" id="rate"></div>
  </div>

    <div class = "currency">
      <select id="currency-two">
        <option value="AED">AED</option>
          <option value="ARS">ARS</option>
          <option value="AUD">AUD</option>
          <option value="BGN">BGN</option>
          <option value="BRL">BRL</option>
          <option value="BSD">BSD</option>
          <option value="CAD">CAD</option>
          <option value="CHF">CHF</option>
          <option value="CLP">CLP</option>
          <option value="CNY">CNY</option>
          <option value="COP">COP</option>
          <option value="CZK">CZK</option>
          <option value="DKK">DKK</option>
          <option value="DOP">DOP</option>
          <option value="EGP">EGP</option>
          <option value="EUR">EUR</option>
          <option value="FJD">FJD</option>
          <option value="GBP">GBP</option>
          <option value="GTQ">GTQ</option>
          <option value="HKD">HKD</option>
          <option value="HRK">HRK</option>
          <option value="HUF">HUF</option>
          <option value="IDR">IDR</option>
          <option value="ILS">ILS</option>
          <option value="INR">INR</option>
          <option value="ISK">ISK</option>
          <option value="JPY">JPY</option>
          <option value="KRW">KRW</option>
          <option value="KZT">KZT</option>
          <option value="MXN">MXN</option>
          <option value="MYR">MYR</option>
          <option value="NOK">NOK</option>
          <option value="NZD">NZD</option>
          <option value="PAB">PAB</option>
          <option value="PEN">PEN</option>
          <option value="PHP">PHP</option>
          <option value="PKR">PKR</option>
          <option value="PLN">PLN</option>
          <option value="PYG">PYG</option>
          <option value="RON">RON</option>
          <option value="RUB">RUB</option>
          <option value="SAR">SAR</option>
          <option value="SEK">SEK</option>
          <option value="SGD">SGD</option>
          <option value="THB">THB</option>
          <option value="TRY">TRY</option>
          <option value="TWD" selected>TWD</option>
          <option value="UAH">UAH</option>
          <option value="USD">USD</option>
          <option value="UYU">UYU</option>
          <option value="VND">VND</option>
          <option value="ZAR">ZAR</option>
      </select>
      <input type ="number" id="amount-two" placeholder="0">
    </div>
  <script src="script.js">
          
  </script>
</body>
</html>
```

## CSS的結構
重點: 
1. 為了確保色彩統一，這邊使用一個`根元素 :root`來定義主題顏色
2. 讓列表有箭頭符號，使用link去連結樣式
3. 使用@media (max-width: 600px)，讓螢幕寬度小於600時，改變輸入框的大小將會被調整。

```css=
:root {
  --primary-color: #5fbaa7;
}

*{
  box-sizing: border-box;
}

body{
  background-color: #f4f4f4;
  font-family: Arial, Helvetica, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: cneter;
  height: 100vh;
  margin: 0;
  padding: 20px;
}

h1{
  color: var(--primary-color);
}

p{
  text-align: center;
}

.btn {
  color: #fff;
  background: var(--primary-color);
  cursor: pointer;
  border-radius: 5px;
  font-size: 12px;
  padding: 5px 12px;
}

.money-img {
  width: 150px;
}

.currency {
  padding: 40px 0;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.currency select {
  padding: 10px 20px 10px 10px;
  -moz-appearance: none;
  -webkit-appearance: none;
  appearance: none;
  border: 1px solid #dedede;
  font-size: 16px;
  background: transparent;
  background-image: url('data:image/svg+xml;charset=US-ASCII,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%22292.4%22%20height%3D%22292.4%22%3E%3Cpath%20fill%3D%22%20000002%22%20d%3D%22M287%2069.4a17.6%2017.6%200%200%200-13-5.4H18.4c-5%200-9.3%201.8-12.9%205.4A17.6%2017.6%200%200%200%200%2082.2c0%205%201.8%209.3%205.4%2012.9l128%20127.9c3.6%203.6%207.8%205.4%2012.8%205.4s9.2-1.8%2012.8-5.4L287%2095c3.5-3.5%205.4-7.8%205.4-12.8%200-5-1.9-9.2-5.5-12.8z%22%2F%3E%3C%2Fsvg%3E');
  background-position: right 10px top 50%, 0, 0;
  background-size: 12px auto, 100%;
  background-repeat: no-repeat;
}

.currency input {
  border: 0;
  background: transparent;
  font-size: 30px;
  text-align: right;
}

.swap-rate-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.rate {
  color: var(--primary-color);
  font-size: 14px;
  padding: 0 10px;
}

select:focus,
input:focus,
button:focus {
  outline: 0;
}

@media(max-width: 600px) {
  .currency input {
    width: 200px;
  }
}
```

## Javascript的結構
重點:
1. 使用fetch來對API發出請求，並且設計一個function，來把請求到的值(匯率)與幣別進行運算
2. 使用change和input的時機
[參考資料_MDN Change的解說](https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/change_event)

`Change`
當input、select或textarea的元素被user下達指令(commit)且改變後，事件會被觸發
所以適合用來作為下拉式選單的選項被點選後的動作

`Input`
input則會在內容有所變更時就會變化，所以用在自動產出匯率總和部分較為合適


```javascript=
//宣告與定義變數，連接Javascript與HTML
const currencyEl_one = document.getElementById('currency-one');
const amountEl_one = document.getElementById('amount-one');
const currencyEl_two = document.getElementById('currency-two');
const amountEl_two = document.getElementById('amount-two');

const rateEl = document.getElementById('rate');
const swap = document.getElementById('swap');

// Fetch exchange rates and update the DOM
function calculate() {
  const currency_one = currencyEl_one.value;
  const currency_two = currencyEl_two.value;

  fetch(`https://api.exchangerate-api.com/v4/latest/${currency_one}`)
    .then(res => res.json())
    .then(data => {
      const rate = data.rates[currency_two];
      rateEl.innerText=`1 ${currency_one} = ${rate} ${currency_two}`;

      amountEl_two.value= (amountEl_one.value * rate).toFixed(2);
    });
}

// Event listeners
currencyEl_one.addEventListener('change', calculate);
amountEl_one.addEventListener('input', calculate);
currencyEl_two.addEventListener('change', calculate);
amountEl_two.addEventListener('input', calculate);

swap.addEventListener('click', () => {
  const temp = currencyEl_one.value;
  currencyEl_one.value=currencyEl_two.value;
  currencyEl_two.value=temp;
  calculate();
});


calculate();
```