19、javascript基础知识

1、几天接到了一个奇葩的需求，就是在鼠标滚轮滑动的时候，div要悬浮不动，因此这引起了我对于javascript知识的复习

首先从最基础的变量的类型开始

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
    alert(undefined == null);
</script>
</head>
<body>

以上alert会显示true

2、全选，全不选和反选感觉个人真的不是对代码有依赖，感觉如果能不敲代码就真的棒级了，因此将来想回家帮妈妈买货，感觉能

靠嘴挣钱总比，动手强

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <br />
    <input type="checkbox" name="items" value="足球">足球
    <input type="checkbox" name="items" value="篮球">篮球
    <input type="checkbox" name="items" value="排球">排球
    <input type="checkbox" name="items" value="谭倩">谭倩
    <br />
    <input type="button" id="checkAll" value="全选">
    <input type="button" id="nocheckAll" value="全不选">
    <input type="button" id="oppositeAll" value="反选">
    <script type="text/javascript">
        var checkButton = document.getElementById("checkAll");
        checkButton.onclick = function() {
            var items = document.getElementsByName("items");
            for (var i = 0; i < items.length; i++) {
                if (!items[i].checked) {
                    items[i].checked = true;
                }
            }
        }
        var nocheckButton = document.getElementById("nocheckAll");
        nocheckButton.onclick = function() {
            var items2 = document.getElementsByName("items");
            for (var i = 0; i < items2.length; i++) {
                if (items2[i].checked) {
                    items2[i].checked = false;
                }
            }
        }
        var oppcheckButton = document.getElementById("oppositeAll");
        oppcheckButton.onclick = function() {
            var items3 = document.getElementsByName("items");
            for (var i = 0; i < items3.length; i++) {
                if (items3[i].checked) {
                    items3[i].checked = false;
                } else {
                    items3[i].checked = true;
                }
            }
        }
    </script>

</body>
</html>

3、点击关上，点击打开

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<style type="text/css">
div {
    display: none;
}

a {
    background-color: orange;
}

.open {
    display: block;
}

.close {
    display: none;
}
p{
    font: bolder;
    font-family: cursive;
    font-style: italic;
    color: blue;
    background-color: orange;
}
table, tr, td {
    padding: 0px;
}
</style>
<script type="text/javascript">
    function openDiv(a) {
        var currentDiv = a.parentNode.getElementsByTagName("div")[0];
        var divs = document.getElementsByTagName("div");
        for (var i = 0; i < divs.length; i++) {
            if (currentDiv == divs[i]) {
                currentDiv.className = "open";
            } else {
                divs[i].className = "close";
            }
        }
    }
</script>
</head>
<body>
    <table>
        <tr>
            <td><a onclick="openDiv(this)">高中同学</a>
                <div>
                    <p>大勇</p> <p>君宇</p> <p>茂川</p>
                </div></td>
        </tr>
        <tr>
            <td><a onclick="openDiv(this)" >初中同学</a>
                <div>
                    <p>浩晨</p> <p>孟凯妮</p> <p>李倩</p>
                </div></td>
        </tr>
        <tr>
            <td><a onclick="openDiv(this)">小学同学</a>
                <div>
                    <p>想不起来了</p>

                </div></td>
        </tr>
        <tr>
            <td><a onclick="openDiv(this)">大学同学</a>
                <div>
                    <p>王金鉴</p> <p>李俊峰</p> <p>王宝林</p>
                </div></td>
        </tr>
    </table>
</body>
</html>