新手村15 - LocalStorage

11th鐵人賽 javascript 前端新手村

Chester

2019-09-30 14:57:30

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15 - LocalStorage

俗話說的好，一天一蘋果，醫生遠離我

一天一 JS，What the f*ck JavaScript？

small steps every day - 記錄著新手村日記

完成目標

localStorage
event delegation

功能
- 做一個可以輸入文字的框，送出之後新增一個 Checkbox
- 重新整理時，選單不會清空會存進 localStorage
畫面
- 選單的選項前面，要有打勾的功能，並且自訂圖示

index_START.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>LocalStorage</title>
  <link rel="stylesheet" href="style.css">
</head>
<body>
   <!--
      Fish SVG Cred:
      https://thenounproject.com/search/?q=fish&i=589236
   -->

   <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" x="0px" y="0px" viewBox="0 0 512 512" enable-background="new 0 0 512 512" xml:space="preserve"><g><path d="M495.9,425.3H16.1c-5.2,0-10.1,2.9-12.5,7.6c-2.4,4.7-2.1,10.3,0.9,14.6l39,56.4c2.6,3.8,7,6.1,11.6,6.1h401.7   c4.6,0,9-2.3,11.6-6.1l39-56.4c3-4.3,3.3-9.9,0.9-14.6C506,428.2,501.1,425.3,495.9,425.3z M449.4,481.8H62.6L43,453.6H469   L449.4,481.8z"/><path d="M158.3,122c7.8,0,14.1-6.3,14.1-14.1V43.4c0-7.8-6.3-14.1-14.1-14.1c-7.8,0-14.1,6.3-14.1,14.1v64.5   C144.2,115.7,150.5,122,158.3,122z"/><path d="M245.1,94.7c7.8,0,14.1-6.3,14.1-14.1V16.1c0-7.8-6.3-14.1-14.1-14.1C237.3,2,231,8.3,231,16.1v64.5   C231,88.4,237.3,94.7,245.1,94.7z"/><path d="M331.9,122c7.8,0,14.1-6.3,14.1-14.1V43.4c0-7.8-6.3-14.1-14.1-14.1s-14.1,6.3-14.1,14.1v64.5   C317.8,115.7,324.1,122,331.9,122z"/><path d="M9.6,385.2c5.3,2.8,11.8,1.9,16.2-2.2l50.6-47.7c56.7,46.5,126.6,71.9,198.3,71.9c0,0,0,0,0,0   c87.5,0,169.7-36.6,231.4-103.2c5-5.4,5-13.8,0-19.2c-61.8-66.5-144-103.2-231.4-103.2c-72,0-142.2,25.6-199,72.5l-50-47.1   c-4.4-4.1-10.9-5-16.2-2.2c-5.3,2.8-8.3,8.7-7.4,14.6l11.6,75L2.2,370.6C1.3,376.5,4.2,382.4,9.6,385.2z M380.9,230.8   c34.9,14.3,67.2,35.7,95.3,63.6c-10.1,10-20.8,19.2-31.9,27.5c-22.4-3.3-29.6-8.8-30.7-9.7c-4-5.7-11.8-7.7-18.1-4.4   c-6.9,3.6-9.5,12.2-5.9,19.1c1.9,3.5,7.3,10.3,22.4,16c-10.1,5.7-20.5,10.7-31.1,15.1C352.4,320.2,352.4,268.6,380.9,230.8z    M36.3,255.6l29.4,27.7c5.3,5,13.6,5.1,19.1,0.3c53.2-47.6,120.7-73.7,190-73.7c26.9,0,53.2,3.9,78.5,11.3   c-29.3,44.6-29.3,102,0,146.6c-25.3,7.4-51.6,11.3-78.5,11.3c-69,0-136.3-26-189.4-73.2c-2.7-2.4-13.4-6.3-19.1,0.3l-30.1,28.3   l5.7-40C42.2,293,36.3,255.6,36.3,255.6z"/><circle cx="398.8" cy="273.8" r="14.1"/></g></svg>

  <div class="wrapper">
    <h2>LOCAL TAPAS</h2>
    <p></p>
    <ul class="plates">
      <li>Loading Tapas...</li>
    </ul>
    <form class="add-items">
      <input type="text" name="item" placeholder="Item Name" required>
      <input type="submit" value="+ Add Item">
    </form>
  </div>

<script>
  const addItems = document.querySelector('.add-items');
  const itemsList = document.querySelector('.plates');
  const items = [];
</script>

</body>
</html>

CSS

html {
  box-sizing: border-box;
  background: url('http://wes.io/hx9M/oh-la-la.jpg') center no-repeat;
  background-size: cover;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  text-align: center;
  font-family: Futura,"Trebuchet MS",Arial,sans-serif;
}

*, *:before, *:after {
  box-sizing: inherit; 
}

svg {
  fill:white;
  background: rgba(0,0,0,0.1);
  padding: 20px;
  border-radius: 50%;
  width: 200px;
  margin-bottom: 50px;
}

.wrapper {
  padding: 20px;
  max-width: 350px;
  background: rgba(255,255,255,0.95);
  box-shadow: 0 0 0 10px rgba(0,0,0,0.1);
}

h2 {
  text-align: center;
  margin: 0;
  font-weight: 200;
}

.plates {
  margin: 0;
  padding: 0;
  text-align: left;
  list-style: none;
}

.plates li {
  border-bottom: 1px solid rgba(0,0,0,0.2);
  padding: 10px 0;
  font-weight: 100;
  display: flex;
}

.plates label {
  flex: 1;
  cursor: pointer;
}

.plates input {
  display: none;
}

.plates input + label:before {
  content: '⬜️';
  margin-right: 10px;
}

.plates input:checked + label:before {
  content: '?';
}

.add-items {
  margin-top: 20px;
}

.add-items input {
  padding: 10px;
  outline: 0;
  border: 1px solid rgba(0,0,0,0.1);
}

JS - step by step

首先開始前先將最後完成檔copy一份先把資料add到本地端的localStorage，方便等等開始寫來 console 。在這個範例檔當中，我們將從 localStorage 抓到的資料設為變數 items 後，產生出 HTML 塞進Class plates 之中，值得一提的是，我們該如何抓到資料、資料不會是空的造成 undefined 呢？

在 localStorage 中，需要了解抓資料跟存資料的兩種方法： getItem、setItem ，並因為抓出來的一個字串，因此透過之前所提過的 JSON.parse() 轉換為物件，為了確保 undefined 的問題，如果抓不到的資料的話預設為空陣列

Storage.getItem()：https://tinyurl.com/mfx39k9

JSON.parse()：https://tinyurl.com/y48zz9vd

<script>
  const addItems = document.querySelector('.add-items');
  const itemsList = document.querySelector('.plates');
  const items = JSON.parse(localStorage.getItem('items')) || [];

  function populateList(plates = [], platesList) {
    platesList.innerHTML = plates.map((plate, i) => {
      return `
        <li>
          <input type="checkbox" data-index="${i}" id="item${i}" 
											 ${plate.done ? 'checked' : ''} />
          <label for="item${i}">${plate.text}</label>
        </li>
      `;
    }).join('');
  }

  populateList(items, itemsList);
</script>

接下來，我們來寫 addItem 的function，首先我們應該將輸入的資料抓到後 push 進去變數中 items.push(item) ，並且再次更新畫面 populateList(items, itemsList) 、更新資料 localStorage.setItem('items', JSON.stringify(items)) ，將輸入的數值重整不要停留在畫面上this.reset();

Event.preventDefault()：https://tinyurl.com/kkh9hmd

<script>
 // 上略
 function addItem(e) {
     e.preventDefault();
     const text = (this.querySelector('[name=item]')).value;
     const item = {
       text,
       done: false
     };

     items.push(item);
     populateList(items, itemsList);
     localStorage.setItem('items', JSON.stringify(items));
     this.reset();
   }

   addItems.addEventListener('submit', addItem);
</script>

與上方的概念相同，我們有個 toggleDone 的function

<script>
	// 上略
  function toggleDone(e) {
      if (!e.target.matches('input')) return; // skip this unless it's an input
      const el = e.target;
      const index = el.dataset.index;
      items[index].done = !items[index].done;
      localStorage.setItem('items', JSON.stringify(items));
      populateList(items, itemsList);
    }

  itemsList.addEventListener('click', toggleDone);
</script>

就大功告成啦！

JS - final

<script>
  const addItems = document.querySelector('.add-items');
  const itemsList = document.querySelector('.plates');
  const items = JSON.parse(localStorage.getItem('items')) || [];

  function addItem(e) {
    e.preventDefault();
    const text = (this.querySelector('[name=item]')).value;
    const item = {
      text,
      done: false
    };

    items.push(item);
    populateList(items, itemsList);
    localStorage.setItem('items', JSON.stringify(items));
    this.reset();
  }

  function populateList(plates = [], platesList) {
    platesList.innerHTML = plates.map((plate, i) => {
      return `
        <li>
          <input type="checkbox" data-index=${i} id="item${i}" ${plate.done ? 'checked' : ''} />
          <label for="item${i}">${plate.text}</label>
        </li>
      `;
    }).join('');
  }

  function toggleDone(e) {
    if (!e.target.matches('input')) return; // skip this unless it's an input
    const el = e.target;
    const index = el.dataset.index;
    items[index].done = !items[index].done;
    localStorage.setItem('items', JSON.stringify(items));
    populateList(items, itemsList);
  }

  addItems.addEventListener('submit', addItem);
  itemsList.addEventListener('click', toggleDone);

  populateList(items, itemsList);

</script>

本刊同步於個人網站：http://chestertang.site/

本次範例程式碼原作者來源：https://tinyurl.com/yavm5f5n