用JavaScript写一个能开始和暂停的时钟

//sScript
var showTime = document.getElementById('seconds')
        var id =0
        function fn(){
            var i = 0
            var s = 0
            var m = 0
            var h = 0
             id =setInterval(function(){
                i++
                s = fn2(i%60)
                m = fn2(parseInt(i/60%60))
                h = fn2(parseInt(i/3600%24))
                showTime.innerHTML = `${h}小时 ${m}分钟 ${s}秒`
            },1000)
        }

        function fn2(number){
            if(number<10){
                return '0'+ number
            }
            return number
        }
        function fn3(){
            clearInterval(id)
        }

//HTML
<b id="seconds">00:00:00</b>
<button id="btn" onclick="fn()">点下试试</button>
<button id="btn2" onclick="fn3()">清除</button>