暂停键停止不了，求大神

Question

类似轮播图

<input type="button" id="btn1" value="开始" />
	<input type="button" id="btn2" value="暂停" />
	<div id="yanse" style="width: 200px; height: 200px;border: dashed;">
	</div>
	<script type="text/javascript">
	var obtn1=document.getElementById("btn1")	
	var obtn2=document.getElementById("btn2")	
	var oyanse=document.getElementById("yanse")	
	var timer=null
	var n=0
	var arr=["red","green","yellow","bule"]
	obtn1.onclick=function  () {
		timer=setInterval(shijian,1000)
	}
	function shijian () {
	clearInterval(timer)
		oyanse.style.backgroundColor=arr[n]
		n++
		n=n%arr.length
	}
	obtn2.onclick=function  () {
		clearInterval(timer)
	}
	</script>
	

Answer 1

<input type="button" id="btn1" value="开始" />
<input type="button" id="btn2" value="暂停" />
<div id="yanse" style="width: 200px; height: 200px;border: dashed;">
</div>

<script type="text/javascript">
  var obtn1 = document.getElementById("btn1")
  var obtn2 = document.getElementById("btn2")
  var oyanse = document.getElementById("yanse")
  var timer = null
  var n = 0
  var arr = ["red", "green", "yellow", "bule"]
  obtn1.onclick = function () {
    timer = setInterval(shijian, 1000)
  }
  function shijian() {
    //这一行删除
    oyanse.style.backgroundColor = arr[n]
    n++
    n = n % arr.length
  }
  obtn2.onclick = function () {
    clearInterval(timer)
  }
</script>