javascript的基础交互详解

  var box = document.getElementById("box1");
        console.log(box);//<div id="box1">我是DIV</div>
        var box = document.getElementById("box2");
        console.log(box); //null
        var myH2 = document.getElementById("my-h2");
        console.log(myH2);

 var tests = document.getElementsByClassName("test");
        console.log(tests);
        console.log(tests.length); //获取长度
        // 直接输出到控制台
        console.log(tests[0]);
        console.log(tests[1]);
        console.log(tests[tests.length - 1]);
        // 存储起来
        var oDiv = tests[0];
        var oH2 = tests[1];
        console.log(oDiv, oH2);
        var test1 = document.getElementsByClassName("test1");
        console.log(test1, test1.length);
        console.log(test1[0]);
        console.log(test1[1]); //没有这个小标或索引 相当于集合中这个位置还没有初始化，或未定义 返回undefined
        var hello = document.getElementsByClassName("hello");
        console.log(hello, hello.length);
        console.log(hello[0]); //undefined

   var oLis = document.getElementsByTagName("li");
        console.log(oLis);
        // 获取长度
        console.log(oLis.length);
        // 获取具体的元素
        console.log(oLis[0]);
        console.log(oLis[1]);
        console.log(oLis[2]);
        console.log(oLis[oLis.length - 1]);

// 获取ol下的li
        // 获取父级元素
        var wrap = document.getElementById("wrap");
        console.log(wrap);
        // var oLis = wrap.getElementsByClassName("test");
        var oLis = wrap.getElementsByTagName("li");
        console.log(oLis);
        console.log(oLis.length);
        console.log(oLis[0]);
        console.log(oLis[1]);
        console.log(oLis[oLis.length - 1]);
        // 获取ul下的li
        // 获取父级
        var wrap1 = document.getElementsByClassName("wrap");
        console.log(wrap1);
        console.log(wrap1[0]);
        console.log(wrap1[1]);
        // var ullis = wrap1[1].getElementsByClassName("test");
        var ullis = wrap1[1].getElementsByTagName("li");
        console.log(ullis);
        console.log(ullis.length);
        console.log(ullis[0]);
        console.log(ullis[1]);
        console.log(ullis[ullis.length - 1]);

  <div id="box"></div>
    <ul id="myUl">
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>
    <script>
   var box = document.getElementById("box");
   console.log(box);
   var myUl = document.getElementById("myUl")
   console.log(myUl);
   var oLis = myUl.getElementsByTagName("li");
   console.log(oLis);
            // - onclick  单击事件
            box.onclick = function() {
                console.log("单击");
            }
            // - ondblclick  双击事件
            oLis[0].ondblclick = function() {
                console.log("双击事件");
            }
            // - onmousedown 鼠标按下
            oLis[1].onmousedown = function() {
                console.log("鼠标按下");
            }
            // - onmouseup  鼠标抬起
            oLis[1].onmouseup = function() {
                console.log("鼠标抬起");
            }
            // - onmousemove 鼠标移动
            oLis[1].onmousemove= function() {
                console.log("鼠标移动");
            }
            // - oncontextmenu 鼠标右击
            oLis[2].oncontextmenu = function() {
                console.log("鼠标右击");
            }
            // - onmouseover 鼠标移入
            myUl.onmouseover = function() {
                console.log("鼠标移入");
            }
            // - onmouseout 鼠标移出
            myUl.onmouseout = function() {
                console.log("鼠标移出");
            }
            // - onmouseenter  鼠标进入
            myUl.onmouseenter = function() {
                console.log("鼠标进入");
            }
            // - onmouseleave  鼠标离开
            myUl.onmouseleave = function() {
                console.log("鼠标离开");
            }
    </script>

// 获取元素
var inputs = document.getElementsByTagName("input");
var btn = document.getElementsByTagName("button")[0];
console.log(inputs, btn);
// 将两个输入框的和展示到第三个输入框
// 绑定事件
// 事件每点击一次 函数中代码就重新执行一次
btn.onclick = function () { //做什么事情
    // 获取两个输入框的值
    var oneVal = inputs[0].value;
    var twoVal = inputs[1].value;
    console.log(oneVal, twoVal);
    // 遇到字符串表示拼接 先转为数字
    var total = parseFloat(oneVal) + parseFloat(twoVal);
    console.log(total);
    // 将和设置给第三个输入框
    inputs[2].value = total;
}

var div = document.getElementsByTagName("div")[0];
var h2 = document.getElementsByTagName("h2")[0];
var p = document.getElementsByTagName("p")[0];
console.log(div, h2,p);
// 设置：表单元素.innerText/innHTML = 值;
// 后边设置的覆盖前边的
// div.innerText = "我是div";
// div.innerText = "<h6>我是div</h6>";
// div.innerHTML = "我是div";
div.innerHTML = "<h6><a href='https://www.baidu.com'>我是div</a></h6>";
h2.innerHTML = "我是H2";
// 获取：表单元素.innerText/innHTML;  
console.log(div.innerText);//我是div
console.log(div.innerHTML);//<h6><a href="Https://www.baidu.com">我是div</a></h6>
console.log(p.innerText);
console.log(p.innerHTML);

// 获取元素
var div =  document.getElementsByTagName("div")[0];
// 设置
div.className = "myBox";
div.title = "我是div";
// 获取
console.log(div.id);
console.log(div.className);
console.log(div.title);