浅谈JavaScript_DOM学习篇_图片切换小案例

2019-11-19 11:58:33

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今天开始学习DOM操作,下面写一个小案例来巩固下知识点.

DOM: document object model (文档对象模型)

根据id获取页面元素 :　如:　var xx = document.getElementById("id");

根据标签获取元素:　如:　var xx = document.getElementsByTagName("div");

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Title</title>  <style>    * {      margin: 0;      padding: 0;    }    #outer {      width: 500px;      /*设置上边距50px 水平居中*/      margin: 50px auto;      /*设置边框*/      padding: 10px;      background-color: greenyellow;      /*设置文本居中*/      text-align: center;    }    img {      width: 500px;    }  </style>  <script>　　　　　//btn 为按钮id  clickEventFunction 为点击后执行的操作函数    function addClick(btn, clickEventFunction) {      var myButton = document.getElementById(btn);      myButton.onclick = clickEventFunction;    };    window.onload = function () {      (function () {        var pics = ["imgs/1.png",          "imgs/2.png",          "imgs/3.png"];        var index = 0;        showPicNum(index);        var img = document.getElementsByTagName("img")[0];        // var btn1 = document.getElementById("btn1");        var btn2 = document.getElementById("btn2");        addClick("btn1", function () {          index--;          if (index <= -1) {            index = pics.length - 1;          }          console.log(index + " ----- ");          img.src = pics[index];          showPicNum(index);        });        addClick("btn2", function () {          index++;          if (index >= pics.length) {            index = 0;          }          console.log(index + " ++++++++ ");          img.src = pics[index];          showPicNum(index);        });        //        // btn1.onclick = function () {        //   index --;        //   if(index <= -1){        //     index = pics.length - 1;        //   }        //   console.log(index + " ----- ");        //   img.src = pics[index];        //   showPicNum(index);        // };        // btn2.onclick = function () {        //   index ++;        //   if(index >= pics.length){        //     index = 0;        //   }        //   console.log(index + " ++++++++ ");        //   img.src = pics[index];        //   showPicNum(index);        // };        console.log(index);        /**         * 展示当前图片为第几张         * @param index  当前图片索引         */        function showPicNum(index) {          var descrs = document.getElementById("discs");          descrs.innerText = "一共" + pics.length + "张图片,当前第" + ++index + "张";        }      }())    };  </script></head><body><div id="outer">  <p id="discs"></p>  <img src="imgs/1.png"/><br>  <button id="btn1" type="button" value="上一张">上一张</button>  <button id="btn2" type="button" value="下一张">下一张</button></div></body></html>

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