Not able to define "var" in replace() method - Javascript

Question

I am trying to use var in replace method. See below code, I wanted to replace all "xyz" from myString.

var myString = "abc qwer xyz abc qwer xyz abc qwer xyz";
var myNewString = myString.replace(/xyz/g,"");
console.log(myNewString);

Output: abc qwer abc qwer abc qwer

But when I define variable for "xyz" it is not recognizing it.

var myString = "abc qwer xyz abc qwer xyz abc qwer xyz";
var setWord = "xyz";
var myNewString = myString.replace(/setWord/g,"");
console.log(myNewString);

Output: abc qwer xyz abc qwer xyz abc qwer xyz

Can anyone help me to understand why I am not able to define variable in replace method along with Regular Expression.