const animals = [
    {
        "name": "cat",
        "size": "small",
        "weight": 5
    },
    {
        "name": "dog",
        "size": "small",
        "weight": 10
    },
    {
        "name": "lion",
        "size": "medium",
        "weight": 150
    },
    {
        "name": "elephant",
        "size": "big",
        "weight": 5000
    }
];

// Map - do same operation on each array element, return an array of same size
animals.map(animal => animal.name);
// ["cat", "dog", "lion", "elephant"]

// Filter - return array that matching certain criteria
animals.filter(animal => animal.size === "small");
/*
[
  {
    "name": "cat",
    "size": "small",
    "weight": 5
  },
  {
    "name": "dog",
    "size": "small",
    "weight": 10
  }
]
*/

// Reduce - use the values in an array and return something completely new
animals.reduce((weight, animal) => {return weight += animal.weight}, 0);
// 5165