// ES5
var arrayObjects = [
  {
    id: 1,
    name: "A"
  },
  {
    id: 2,
    name: "B"
  },
  {
    id: 3,
    name: "C"
  }
];

Array.prototype.map.call(arrayObjects, function(item) { return item.id; }).join(","); // "1,2,3"


// ES6 / TypeScript
const arrayObjects = [
  {
    id: 1,
    name: "A"
  },
  {
    id: 2,
    name: "B"
  },
  {
    id: 3,
    name: "C"
  }
];
Array.prototype.map.call(arrayObjects, s => s.id).toString(); // "1,2,3"