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文本框根据输入内容自适应高度的代码

2011-10-24 00:00 591 查看
其实现代浏览器大多都支持文本框尺寸调节功能,绝大多数情况下却没有自动适应来得爽快,在网络上发现一方法比较简单的实现文本框高度自适应,于是封装了这个函数,准备以后应用到项目中。
源代码:
23:03文章更新:
感谢alucelx同学再次给力的帮助,大大简化了方法,更新代码为0.2版本,同时解决了兼容Opera浏览器,至此全兼容IE6+与现代浏览器!
在线演示: http://demo.jb51.net/js/2011/autoArea/index.htm
autoTextarea.js
/** 
* 文本框根据输入内容自适应高度 
* @author tang bin 
* @version 0.3 
* @see http://www.planeart.cn/?p=1489 
* @param {HTMLElement} 输入框元素 
* @param {Number} 设置光标与输入框保持的距离(默认20) 
* @param {Number} 设置最大高度(可选) 
*/ 
var autoTextarea = function (elem, extra, maxHeight) { 
extra = extra || 20; 
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.maxHeight = 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(); 
};

测试代码:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>文本框根据输入内容自适应高度</title>
<style type="text/css">
#textarea { font: 1.4em/1.8em Arial; overflow: hidden; width: 550px; height: 6em; padding:10px; }
</style>
<script src="autoTextarea.js"></script>
</head>
<body style="background:#FBFCFD url(http://goo.gl/kLsZX);">
<textarea id="textarea"></textarea>
<script>
var text = document.getElementById("textarea"),
tip = '想写点什么..';
autoTextarea(text);// 调用
text.value = tip;
text.onfocus = function () {
if (text.value === tip) text.value = '';
};
text.onblur = function () {
if (text.value === '') text.value = tip;
};
</script>
</body>
</html>
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