# 小專案五: DOM Array Methods | Array的應用
###### tags: `JS小專案`
## 成品示意圖
## 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();
```
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