推荐使用：
/**
* textarea高度自动适应内容的高度
* @param obj dom 元素，可以是 $('#content')[0] 或者 document.getElementById('content')
*/
function autoTextAreaHeight(obj) {
let style = window.getComputedStyle(obj, null);
obj.style.height = obj.scrollTop + obj.scrollHeight - parseFloat(style.getPropertyValue('padding-top')) - parseFloat(style.getPropertyValue('padding-bottom')) + 'px';
}
然后在需要调用的页面输入如下代码：
$(function () {
var infoTextarea = $('#info');//textarea的id属性为info
infoTextarea.on('input', function () {
autoTextAreaHeight(infoTextarea[0]);
});
autoTextAreaHeight(infoTextarea[0]);
});
下面是在网络上发现的一个封装函数，全兼容IE6+与现代浏览器！具体函数代码如下（可以看看实现方法，不推荐使用）：
/**
* 文本框根据输入内容自适应高度
* @author tang bin
* @version 0.3
* @see https://www.maopiaopiao.com/jquery/32.html
* @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();
};
调用方法如下（textarea_id为textarea的id值）：
autoTextarea(document.getElementById('textarea_id'));
另外一种简易的实现方法：
<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>TEXTAREA自适应文字行数的多少</title> </head> <body> <textarea rows="6" name="s1" cols="27" onpropertychange="this.style.posHeight=this.scrollHeight"></textarea> </body> </html>