JavaScript splice() 步骤第三个参数无法识别

JavaScript splice() 方法第三个参数无法识别
    菜鸟学习javascript，在数组splice() 方法中写入第三个参数是浏览器就不识别，想请教一下是怎么一回事。我用的是chrome，代码如下。

document.write("<div id='show'>");


		var a=[23,566,3,78,6,633,42,5,7867,34,774,3];

		document.write("a:&nbsp"+a+"</br>");


		//splice第一个参数表示删除位置，第二个表示删除个数

		document.write("<span style='color:green'>a.splice(10):&nbsp"+a.splice(10)+"</span></br>");

		document.write("a:&nbsp"+a+"</br>");

		document.write("<span style='color:red'>a.splice(1,3):&nbsp"+a.splice(1,3)+"</span></br>");

		document.write("a:&nbsp"+a+"</br>");

		document.write("<span style='color:red'>a.splice(3,1):&nbsp"+a.splice(3,1)+"</span></br>");

		document.write("a:&nbsp"+a+"</br>");

		//a.splice(1,1,"b")；这个有问题

		//document.write("<span style='color:yellow'>a.splice(3,1,"a"):&nbsp"+a.splice(3,1,"a")+"</span></br>");

		document.write("a:&nbsp"+a+"</br>");


   		document.write("</div>");

    一旦执行倒数三四浏览器就不显示了。
------解决思路----------------------
document.write("<span style='color:yellow'>a.splice(3,1,\"a\"):&nbsp"+a.splice(3,1,"a")+"</span></br>");
------解决思路----------------------

<script>

document.write("<div id='show'>");

 

        var a=[23,566,3,78,6,633,42,5,7867,34,774,3];

        document.write("a:&nbsp"+a+"</br>");

         

        //splice第一个参数表示删除位置，第二个表示删除个数

        document.write("<span style='color:green'>a.splice(10):&nbsp"+a.splice(10)+"</span></br>");

        document.write("a:&nbsp"+a+"</br>");

        document.write("<span style='color:red'>a.splice(1,3):&nbsp"+a.splice(1,3)+"</span></br>");

        document.write("a:&nbsp"+a+"</br>");

        document.write("<span style='color:red'>a.splice(3,1):&nbsp"+a.splice(3,1)+"</span></br>");

        document.write("a:&nbsp"+a+"</br>");

        a.splice(1,1,"b");//这个有问题

        document.write("<span style='color:yellow'>a.splice(3,1,\"a\"):&nbsp"+a.splice(3,1,"a")+"</span></br>");

        document.write("a:&nbsp"+a+"</br>");

 

           document.write("</div>");

  console.log(1)

</script>