filter-map-reduce.js

var animals = [
  { name: "Waffles", type: "dog", age: 12 },
  { name: "Fluffy", type: "cat", age: 14 },
  { name: "Spelunky", type: "dog", age: 4 },
  { name: "Hank", type: "dog", age: 11 }
];

//  filter dogs
animals = animals.filter(function(animal) {
  return animal.type === "dog";
});
console.log(animals);

//  filter dogs whose age is greater than 4
animals = animals.filter(function(animal) {
  return animal.age > 4;
});
console.log(animals);

//  get names of all dogs whose age is greater than 4
var names = animals.map(function(animal) {
  return animal.name;
});
console.log(names);

//  get average age of animals whose age is greater than 4
var totalAge = animals.map(function(animal) {
  return animal.age;
}).reduce(function(prev, curr) {
  return (prev+curr)/2;
});
console.log(totalAge);