如何去掉str中兩側的數字？

正則方式：

var a = ",1,2,3,4,5,6,7,8,9,10,11,12,13";

var r = /,1(?=,)|,1$/g; //替換其他數字需要把兩個數字都改，如 var r = /,3(?=,)|,3$/g;

var b = a.replace(r,"");

split方式：

var a = ",1,2,3,4,5,6,7,8,9,10,11,12,13";

var r = a.split(",");

var b="";

for(var i=0;i