让按钮变灰

JS实现禁用按钮

                <input type="button" value="prev" name="prev" style="height:19px" onclick="decrease()"></input>                <input type="button" value="next" name="next" style="height:19px" onclick="increase()"></input>

    if(increment < max_bt) {        increment++;        document.getElementById("prev").disabled="";    }    else{        alert("@@");        document.getElementById("next").disabled="disable";        return;    }