old_contents: describe("demo", function() {
      describe("demo reverse", function(){
          it("canary test", function() {
              expect(3+5).toEqual(8);
          });
          it("canary test 2", function() {
              var s = "abc";
              expect(s).toEqual("abc");
          });
          it("demo reverse", function() {
              var s = "abc123";
              var result = myReverse(s);
              expect(result).toEqual("321cba");
          });
      });
  });
  
new_contents: describe("demo", function() {
      describe("demo reverse", function(){
          it("canary test", function() {
              expect(3+5).toEqual(8);
          });
          
          it("demo reverse", function() {
              const s = "abc123";
              const result = myReverse(s);
              expect(result).toEqual("321cba");
          });
      });
  });
  
subject: use const ... still unclear which version is supported