javascript 弹出层（警告框）的制作(css元素居中、javascript元素居中)

柔情只为你懂 2021-11-22 11:10 328阅读 0赞

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDc5NzE4Mg_size_16_color_FFFFFF_t_70]

<!DOCTYPE html>
    <html>
    	<head>
    		<meta charset="utf-8">
    		<title>弹出层的制作</title>
    	</head>
    	<style type="text/css">
    		body { 
    			padding: 0;
    			margin: 0;
    
    		}
    
    		#bg { 
    			position: absolute;
    			width: 100%;
    			height: 100%;
    			background: blanchedalmond;
    			opacity: 0.5;
    			display: none;
    
    		}
    
    		p { 
    			margin: 0 auto;
    			font-size: 30px;
    			background: #00FFFF;
    			width: 130px;
    			height: 50px;
    			cursor: pointer;
    			line-height: 50px;
    			text-align: center;
    		}
    
    		#win { 
    				position: absolute;
    				top: 30%;
    				left: 50%;
    				width: 400px;
    				height: 200px;
    				background: #fff;
    				border: 4px solid #f90;
    				margin: -102px 0 0 -202px;
    				display: none;
    		}
    
    		h2 { 
    			margin: 0;
    			width: 100%;
    			height: 50px;
    			background: skyblue;
    		}
    
    		#close { 
    			float: right;
    			width: 50px;
    			height: 50px;
    			text-align: center;
    			line-height: 50px;
    			display: block;
    			cursor: pointer
    		}
    	</style>
    	<script type="text/javascript">
    		window.onload = function() { 
    			var oBg = document.getElementById("bg");
    			var oBtn = document.getElementById("btn");
    			var oWin = document.getElementById("win");
    			var oClose = document.getElementById("close");
    			oBtn.onclick = function() { 
    				oBg.style.display = "block";
    				oWin.style.display = "block";
    			}
    			oClose.onclick = function() { 
    				oBg.style.display = "none";
    				oWin.style.display = "none";
    			}
    		}
    	</script>
    	<body>
    		<div id="bg"></div>
    		<div id="win">
    			<h2><span id="close">×</span></h2>
    		</div>
    		<p id="btn">弹出层</p>
    	</body>
    </html>

CSS实现绝对定位元素的居中效果

position: absolute;
    		top: 50%;
    		left: 50%;
    		width: 400px;
    		height: 200px;
    		border: 4px solid #f90;
    		margin: -102px 0 0 -202px;
    		//宽高的一半

javascript实现元素的居中效果

居中的元素的top =（网页高 –元素的高）/ 2;
    
    	居中的元素的left= (网页宽 –元素的宽) /2;
    
    转化为JavaScript的语法为：
    
    	top = (document.body.clientHeight - element.offsetHeight)/2;
    
    	left = (document.body.clientWidth - element.offsetWidth)/2

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