Array ordering of javascript Objects

I am writing a library that implements various sorting algorithms, and everything was fine until I ran an array of objects.

const exec = (array, fnCompare) =>{
    return sort.bubble(array, fnCompare);
  }

  describe('Array Obejetos', ()=> {
    let array_in = [
      {name: "Alex", age: 12},
      {name: "Max", age: 34},
      {name: "Mary", age: 9},
      {name: "Justin", age: 53}
    ];

    let array_out_asc = [
      {name: "Mary", age: 9},
      {name: "Alex", age: 12},
      {name: "Max", age: 34},
      {name: "Justin", age: 53}
    ]

    const fnASC = (a,b) => {
      return a.age < b.age; //linha onde o console reclama que o erro ocorreu
    };

    it('Ordenação crescente', ()=> {
      assert.deepEqual(array_out_asc, exec(array_in, fnASC));
    });
  });

But I end up having the following output in my unit test:

 24 passing (29ms)
  1 failing

  1) Bubble Array Objetos Ordenação crescente:
     TypeError: Cannot read property 'age' of undefined
      at fnASC (test/bubblesort.spec.js:85:23)
      at core/bubble.js:25:10
      at Array.forEach (native)
      at Object.array.forEach [as bubble] (core/bubble.js:24:11)
      at exec (test/bubblesort.spec.js:10:17)
      at Context.<anonymous> (test/bubblesort.spec.js:89:39)

The error says that it was not possible to read the property acts, however if I add a console log within the fnASC function described above it prints the object perfectly. Anyone have any idea what might be happening?