1：有個(gè)小bug茸时，當(dāng)按刪除鍵時(shí)，高度不會(huì)自適應(yīng)縮減

onpropertychange兼容IE

<textarea id="tValue" style="overflow-y:hidden; height:20px;" onpropertychange="this.style.height=this.scrollHeight + 'px'" oninput="this.style.height=this.scrollHeight + 'px'"></textarea>

JQ寫oninput的寫法

$(selector).on("input oninput",function(){
    this.style.height=this.scrollHeight + 'px';
})

2：完美自適應(yīng)

/**
* 文本框根據(jù)輸入內(nèi)容自適應(yīng)高度
* @param                {HTMLElement}           輸入框元素
* @param                {Number}                設(shè)置光標(biāo)與輸入框保持的距離(默認(rèn)0)
* @param                {Number}                設(shè)置最大高度(可選)
*/
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();
};
//調(diào)用
$(function () {
    // 為每一個(gè)textarea綁定事件使其高度自適應(yīng)
    $.each($("textarea"), function(i, n){
        autoTextarea($(n)[0]);
    });
})

3

$(function(){
    $.fn.autoHeight = function(){    
        function autoHeight(elem){
            elem.style.height = 'auto';
            elem.scrollTop = 0; //防抖動(dòng)
            console.log(elem)
            elem.style.height = elem.scrollHeight + 'px';
        }
        this.each(function(){
            autoHeight(this);
            $(this).on('keyup', function(){
                autoHeight(this);
            });
        });     
    }                
    $('textarea').autoHeight();    
})

4

// html
<div class="expandingArea " id="textarea">
  <pre><span></span><br></pre>
  <textarea></textarea>
</div>

// style
.expandingArea { position:relative;}
textarea{position:aboslate;top:0;left:0;}

// js
function makeExpandingArea(container) {
    var area = container.getElementsByTagName('textarea')[0];
    var span = container.getElementsByTagName('span')[0];
    if (area.addEventListener) {
        area.addEventListener('input', function() {
            span.textContent = area.value;
        }, false);
        span.textContent = area.value;
    } else if (area.attachEvent) {
        area.attachEvent('onpropertychange', function() {
            var html = area.value.replace(/\n/g, '<br/>');
            span.innerText = html;
        });
        var html = area.value.replace(/\n/g, '<br/>');
        span.innerText = html;
    }
    if (window.VBArray && window.addEventListener) { //IE9
        area.attachEvent("onkeydown", function() {
            var key = window.event.keyCode;
            if (key == 8 || key == 46) span.textContent = area.value;
        });
        area.attachEvent("oncut", function() {
            span.textContent = area.value;
        }); //處理粘貼
    }
    container.className += "active";
}
var areas = document.getElementById('textarea');
makeExpandingArea(areas);