textarea高度自适应

function autoTextarea (ele, maxHeight) {
    var elem = document.getElementById(ele)
    // html自身的字体大小
    var baseFontSize = parseFloat(document.documentElement.style.fontSize)
    maxHeight = maxHeight * baseFontSize
    // 是否是火狐浏览器
    var isFirefox = !!document.getBoxObjectFor || 'mozInnerScreenX' in window;
    var isOpera = !!window.opera && !!window.opera.toString().indexOf('Opera');

    /**
     * 添加时事件
     * @param type 事件名称
     * @param callback 触发后的回调
     */
    function addEvent (type, callback) {
      elem.addEventListener ? elem.addEventListener(type, callback, false) : elem.attachEvent('on' + type, callback);
    }

    /**
     * 获取元素的样式
     * @param name 待获取的样式名称
     * @returns {*}
     */
    function getStyle (name) {
      if (elem.currentStyle) {
        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;
      } else {
        return getComputedStyle(elem, null)[name];
      }
    }

    var minHeight = parseFloat(getStyle('height'));

    elem.style.resize = 'none';

    /**
     * 修改元素高度
     */
    function change () {
      var scrollTop
      var height
      var padding = 0
      var 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 + '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();
  }

　　做了下移动端的自适应，源代码转载自：https://www.cnblogs.com/leshao/p/6851897.html