--- tags: JS 直播班 - 2023 秋季班 --- # 🏅 Day 26 - addEventListener 事件監聽 ### addEventListener 語法 `.addEventListener()` 前面會放欲選取的元素， `addEventListener()` 內通常會代入兩個參數，第一個參數為事件類型，第二個參數觸發事件後要執行的動作（函式） 範例： HTML ```htmlembedded= <p class="domElement">123</p> ``` JS ```javascript= const domElement = document.querySelector(".domElement"); domElement.addEventListener("click", function(e) { // 觸發時欲執行的程式 console.log(e); // 以此範例來說，點擊 p.domElement 元素時就會印出參數 e（參數名稱可以自訂，這邊定為 e 有 event 的意思） // 此參數為一個事件物件，包含了與此事件有關的屬性 // 可以嘗試觀看 e 的內容 // 像是： // target 屬性為觸發事件時的元素 // type 屬性為觸發事件的類型 }); ``` > 在指定元素（domElement）監聽特定事件（此範例為 click 事件，需使用引號），當該事件觸發時會執行後方函式，函式有一個參數為事件物件 ### 常用事件介紹 1. click：滑鼠點擊元素時會觸發 2. change：當表單內容改變時會觸發 3. scroll：滾動時觸發 > 更多可以再觀看 [文件](https://developer.mozilla.org/zh-TW/docs/Web/Events) 補充： - [MDN 文件](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener) - https://israynotarray.com/javascript/20190919/1187569768/ 問題 --- 監聽下方元素（.plusOne），當點擊「+1」按鈕時，可以讓 sum 的值 +1，並使用 console.log 印出 sum。 HTML ```htmlembedded= <button type="button" class="plusOne">＋1</button> ``` JS ```javascript= let sum = 0; /* 程式碼撰寫 */ ... ``` ## 回報流程 將答案寫在 CodePen 並複製 CodePen 連結貼至底下回報就算完成了喔! 解答位置請參考下圖（需打開程式碼的部分觀看） ![](https://i.imgur.com/vftL5i0.png) <!-- 解答： let sum = 0; /* 程式碼撰寫 */ const plusOne = document.querySelector(".plusOne"); plusOne.addEventListener("click", function() { sum++; console.log(sum); }) --> 回報區 --- | Discord | CodePen / 答案 | |:---------------------:|:--------------------------------------------------------------------------------:| |yuling|[codepen](https://codepen.io/igzdflpu/pen/MWLoQBM)| |pinyi_9|[codepen](https://codepen.io/Wpypy/pen/RwvgQBZ?editors=1111)| |Helen|[codepen](https://codepen.io/milkteamonster/pen/WNPOzGq?editors=1011)| |Allen|[codepen](https://codepen.io/hlctw/pen/LYqLddQ)| |ann6212|[codepen](https://codepen.io/yqmegupa-the-styleful/pen/mdvwxGv?editors=1011)| |cest_jessie|[codepen](https://codepen.io/itsjessiechen/pen/GRzEQqW)| | tanuki5863 | [Codepen](https://codepen.io/tanuki320/pen/VwgWxaR?editors=1011) | | yuan2781 | [Codepen](https://codepen.io/ismebir/pen/rNPwdbz) | | kuanju27 | [Codepen](https://codepen.io/Eero-Chiao/pen/KKJqRZv) | | stone4584 | [Codepen](https://codepen.io/Royen0506/pen/mdvwLzV) | | Uli | [Codepen](https://codepen.io/uli1313/pen/dyaRezE?editors=1011) | | Yijing | [Codepen](https://codepen.io/Yi-Jing-71080635/pen/wvNejQJ?editors=1010) | | Oria | [Codepen](https://codepen.io/kajing/pen/BaMZVZJ?editors=1111) | | claire | [Codepen](https://codepen.io/yi-wen-chen/pen/wvNeXgp) | | 小夏 | [Codepen](https://codepen.io/michaelhsia/pen/dyaRKmO) | |Moreene|[CodePen](https://codepen.io/Moreene/pen/gOqRKBv)| |celinelinnn|[CodePen](https://codepen.io/celinephoebe/pen/yLZXEZd)| | Chia Pin |[CodePen](https://codepen.io/joker-cat/pen/mdvwKgp)| | Eden | [Codepen](https://codepen.io/iseden/pen/dyaRKrW)| | damon0323 | [Codepen](https://codepen.io/swk9eny2/pen/PoVjaVe?editors=1011) | | yuan! 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