jquery 規(guī)定多少秒走完進度條?

jquery 怎么規(guī)定多少秒走完進度條?

<div id="">
        <p></p>
        
    </div><span></span>
    <script type="text/javascript">
        $(function(){
            var i = 0;
            var w = $('p').width()
            var index = setInterval(function(){
                i ++;
                var a = w-i
                $('span').text(i)
                $('p').css({width: a+'px'})
                if(i === 100){
                    clearInterval(index)
                }
            },1000)
        })
    </script>