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The Complete Guide to Modern JavaScript

Sets, WeakSets, Maps and WeakMaps

Learn how to store unique values in sets and much more.

We'll cover the following...

What is a Set? #

A Set is an Object where we can store unique values of any type.

Javascript (babel-node)
// create our set
const family = new Set();
// add values to it
family.add("Dad");
console.log(family);
// Set [ "Dad" ]
family.add("Mom");
console.log(family);
// Set [ "Dad", "Mom" ]
family.add("Son");
console.log(family);
// Set [ "Dad", "Mom", "Son" ]
family.add("Dad");
console.log(family);
// Set [ "Dad", "Mom", "Son" ]

As you can see, at the end we tried to add “Dad” again at line 17, but the Set still remained the same because a Set can only take unique values.

Let’s continue using the same Set and see what methods we can use on it.

Node.js
const family = new Set(["Dad", "Mom", "Son"]);
console.log(family.size);
// 3
console.log(family.keys());
// SetIterator {"Dad", "Mom", "Son"}
console.log(family.entries());
// SetIterator {"Dad", "Mom", "Son"}
console.log(family.values());
// SetIterator {"Dad", "Mom", "Son"}
family.delete("Dad");
console.log(family);
// Set [ "Mom", "Son" ]
family.clear();
console.log(family);
// Set []

As you can see, a Set has a size property and we can delete an item from it or use clear to delete all the items from it.

We can also notice that a Set does not ...