一元运算符 in.reduce() function

Question

I was reading a medium article and came across this code. It returns the object with the most experienced pilot using .reduce() . I can't wrap my head around the expression (oldest.years || 0) . Why not just use (oldest.years ) ?

var pilots = [
  {
    id: 10,
    name: "Poe Dameron",
    years: 14,
  },
  {
    id: 2,
    name: "Temmin 'Snap' Wexley",
    years: 30,
  },
  {
   id: 41,
   name: "Tallissan Lintra",
   years: 16,
 },
 {
   id: 99,
   name: "Ello Asty",
   years: 22,
 }
   ];

var mostExpPilot = pilots.reduce(function (oldest, pilot) {
  return (oldest.years || 0) > pilot.years ? oldest : pilot;
}, {});

console.log(mostExpPilot);

Answer 1

When we look at the documentation of Array.reduce https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce#parameters we can see that this is because the example code has an initialValue of {} which has no years property.

Same would be:

var mostExpPilot = pilots.reduce(function (oldest, pilot) {
  return oldest.years > pilot.years ? oldest : pilot;
}, { years: 0});