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textarea输入框自适应高度

2017-09-27 18:40 169 查看 
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style type="text/css">
h2{
text-align: center;
margin:50px auto;
}
#textarea {
display: block;
margin:0 auto;
overflow: hidden;
width: 550px;
font-size: 14px;
height: 18px;
line-height: 24px;
padding:2px;
}
textarea {
outline: 0 none;
border-color: rgba(82, 168, 236, 0.8);
box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1), 0 0 8px rgba(82, 168, 236, 0.6);
}
</style>
<script>
var autoTextarea = function (elem, extra, maxHeight) {
extra = extra || 0;
var isFirefox = !!document.getBoxObjectFor || 'mozInnerScreenX' in window,
isOpera = !!window.opera && !!window.opera.toString().indexOf('Opera'),
addEvent = function (type, callback) {
elem.addEventListener ?
elem.addEventListener(type, callback, false) :
elem.attachEvent('on' + type, callback);
},
getStyle = elem.currentStyle ? function (name) {
var val = elem.currentStyle[name];

if (name === 'height' && val.search(/px/i) !== 1) {
var rect = elem.getBoundingClientRect();
return rect.bottom - rect.top -
parseFloat(getStyle('paddingTop')) -
parseFloat(getStyle('paddingBottom')) + 'px';
};

return val;
} : function (name) {
return getComputedStyle(elem, null)[name];
},
minHeight = parseFloat(getStyle('height'));

elem.style.resize = 'none';

var change = function () {
var scrollTop, height,
padding = 0,
style = elem.style;

if (elem._length === elem.value.length) return;
elem._length = elem.value.length;

if (!isFirefox && !isOpera) {
padding = parseInt(getStyle('paddingTop')) + parseInt(getStyle('paddingBottom'));
};
scrollTop = document.body.scrollTop || document.documentElement.scrollTop;

elem.style.height = minHeight + 'px';
if (elem.scrollHeight > minHeight) {
if (maxHeight && elem.scrollHeight > maxHeight) {
height = maxHeight - padding;
style.overflowY = 'auto';
} else {
height = elem.scrollHeight - padding;
style.overflowY = 'hidden';
};
style.height = height + extra + 'px';
scrollTop += parseInt(style.height) - elem.currHeight;
document.body.scrollTop = scrollTop;
document.documentElement.scrollTop = scrollTop;
elem.currHeight = parseInt(style.height);
};
};

addEvent('propertychange', change);
addEvent('input', change);
addEvent('focus', change);
change();
};
</script>
</head>
<body>
<h2>文本框根据输入内容自适应高度</h2>
<textarea id="textarea" placeholder="回复内容"></textarea>
<script>
var text = document.getElementById("textarea");
autoTextarea(text);// 调用
</script>
</body>
</html>
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