原生js動態改變dom高度

item參數為要改變高度的dom,
maxHight參數為dom的最大高度,
speed參數為改變高度的速度
function addHeight(item,maxHight,speed){
    var itemHeight =parseInt( item.style.height.replace(/[a-z]/gi,''));
    if(itemHeight<=maxHight){
        itemHeight = itemHeight + 1（每次增加改變像素的值）;
        item.style.height= itemHeight+"px";
        setTimeout(function(){addHeight(item);},speed);
    }
}
function subHeight(item){
    var itemHeight =parseInt( item.style.height.replace(/[a-z]/gi,''));
    if(itemHeight>=0{
        itemHeight = itemHeight -1（每次減小像素的值）;
        item.style.height= itemHeight+"px";
        setTimeout(function(){subHeight(item);},speed);
    }