ECMAScript 6 introduces sets. Sets are collections of values and can be iterated in the order of the insertion of their elements. An important characteristic about sets is that a value can occur only once in a set.
The following snippet shows some basic operations on sets:
var mySet = new Set(); mySet.add(1); mySet.add("Howdy"); mySet.add("foo"); mySet.has(1); // true mySet.delete("foo"); mySet.size; // 2 for (let item of mySet) console.log(item); // 1 // "Howdy"
We discussed briefly that JavaScript arrays are not really arrays in a traditional sense. In JavaScript, arrays are objects that have the following characteristics:
The
length
propertyThe functions that inherit from
Array.prototype
(we will discuss this in the next chapter)Special handling for keys that are numeric keys
When we write an array index as numbers, they get converted to strings—arr[0]
internally becomes arr["0"]
. Due to this, there are a few things that we need to be aware of when we use JavaScript arrays:
Accessing...