Enumeration

The for in statement can loop over all of the property names in an object. The enumeration will include functions and prototype properties.

let fruit = {
    apple: 2,
    orange: 5,
    pear: 1,
  },
  sentence = "I have ",
  quantity;
for (kind in fruit) {
  quantity = fruit[kind];
  sentence += quantity + " " + kind + (quantity === 1 ? "" : "s") + ", ";
}
// The following line removes the trailing comma.
sentence = sentence.substr(0, sentence.length - 2) + ".";
// I have 2 apples, 5 oranges, 1 pear.