JavaScript: Functional Programming for JavaScript Developers

Sets

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 property
• The functions that inherit from Array.prototype (we will discuss this in the next chapter)
• Special handling ...