zoukankan html css js c++ java

【居中】一

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
    <div id="btn" style="margin-top:1000px;">btn</div>
    <div id="box" style="display:none;position:absolute;100px;height:100px;background:#f00"></div>
    <script type="text/javascript">
    function scrollX () {
        var de = document.documentElement;
        return self.pageXOffset ||
            (de && de.scrollLeft) ||
            document.body.scrollLeft;
    }
    function scrollY () {
        var de = document.documentElement;
        return self.pageYOffset ||
            (de && de.scrollTop) ||
            document.body.scrollTop;
    }
    function windowHeight () {
        var de = document.documentElement;
        return self.innerHeight ||
            (de && de.clientHeight) ||
            document.body.clientHeight;
    }
    function windowWidth () {
        var de = document.documentElement;
        return self.innerWidth ||
            (de && de.clientWidth) ||
            document.body.clientWidth;
    }
    function setPos () {
        var t = (windowHeight() - 100)/2 + scrollY(),
            l = (windowWidth() - 100)/2 + scrollX();
        document.getElementById('box').style.top = t + 'px';
        document.getElementById('box').style.left = l + 'px';
        document.getElementById('box').style.display = 'block';
    }
    document.getElementById('btn').onclick = function () {
        setPos();
    };    
    window.onresize = function(){
        setPos();
    }
    </script>
</body>
</html>

by 《精通JavaScript》

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原文地址：https://www.cnblogs.com/jzm17173/p/2526656.html