Interfaces

JavaScript provides some data structures that allow us to manipulate data in an efficient, useful and simply way.

The most important are:

Map

ES6 introduces a new data structure used for mapping keys with values. We can iterate over the elements in them order of insertion.

let myMap = new Map();
myMap.set("dog", "perro");
myMap.set("cat", "gato");
myMap.set("tiger", "tigre");
console.log(myMap.size);            // prints 3.

// Let's iterate over our map
for (let [key, value] of myMap) {
    console.log(key + "-" + value);     // prints dog-perro, cat-gato, ...
}

It's possible that you realize that there is already a structure for mapping like this in JavaScript, an object. But there are some differences between them:

• Keys of an object are of type String, always. Map allows any type of key.
• We can get the size of a Map doing myMap.size, with an object you have to iterate over it or instead use a function called Object.keys(myObject) that will return the keys of an object as an interable.
• Iteration over maps are in the same order that were inserted.

So to get things clear: Use maps when keys are unknown since execution time. Use objects when you have clear entities with differenced key-value pairs.

WeakMap

https://developer.mozilla.org/es/docs/Web/JavaScript/Guide/Keyed_collections

Exercise

Get the legs property and get the data inside the third position of numbers using destructuring. Give it the names of myLegs and thirdPosition respectively.