JavaScript Set Explained Like You're 10

PariSh KhAn — Thu, 23 Jul 2026 17:02:13 +0000

If you have used Python before, you probably already know about set.

When I started using JavaScript Set, I immediately thought:

"Finally! I always wished JavaScript had this."

It solves a very common problem with just one line of code.

Let's learn it with simple examples.

Imagine a Toy Box

You have a toy box.

Every time you put a toy inside, your mom checks one thing.

Is this toy already in the box?

If no, she puts it in.
If yes, she ignores it.

That is exactly how a JavaScript Set works.

A Set only stores unique values.

Creating Your First Set

const toys = new Set();

Now let's add some toys.

toys.add("Car");
toys.add("Robot");
toys.add("Car");

Now print it.

console.log(toys);

Output:

Set(2) { 'Car', 'Robot' }

Even though we added "Car" twice, it only appears once.

That is the magic of Set.

Arrays Can Have Duplicates

const fruits = [
  "Apple",
  "Apple",
  "Orange",
  "Banana",
  "Banana"
];

Output:

Apple
Apple
Orange
Banana
Banana

Sometimes this is what you want.

Sometimes it isn't.

Remove Duplicates Instantly

With Set:

const fruits = [
  "Apple",
  "Apple",
  "Orange",
  "Banana",
  "Banana"
];

const uniqueFruits = new Set(fruits);

console.log(uniqueFruits);

Output:

Set(3) {
  'Apple',
  'Orange',
  'Banana'
}

Only unique values remain.

Convert It Back to an Array

Most of the time you still want an array.

Easy.

const uniqueFruits = [...new Set(fruits)];

Now:

console.log(uniqueFruits);

Output:

[
  "Apple",
  "Orange",
  "Banana"
]

This is probably the most common use of Set.

Check If Something Exists

Instead of writing:

fruits.includes("Apple")

You can do:

const fruits = new Set([
  "Apple",
  "Orange",
  "Banana"
]);

console.log(fruits.has("Apple"));

Output:

true

It reads very naturally.

Remove Something

fruits.delete("Orange");

Now the set contains:

Apple
Banana

Remove Everything

fruits.clear();

Now the set is empty.

Count Items

console.log(fruits.size);

Output:

Notice something?

Arrays use:

array.length

Sets use:

set.size

Loop Through a Set

const colors = new Set([
  "Red",
  "Blue",
  "Green"
]);

for (const color of colors) {
  console.log(color);
}

Output:

Red
Blue
Green

A Real-Life Example

Imagine users enter email addresses.

const emails = [
  "john@gmail.com",
  "john@gmail.com",
  "mary@gmail.com",
  "john@gmail.com",
  "alice@gmail.com"
];

You only want unique emails.

const uniqueEmails = [...new Set(emails)];

Result:

[
  "john@gmail.com",
  "mary@gmail.com",
  "alice@gmail.com"
]

Done.

No complicated loops.

No extra code.

When Should You Use Set?

Set is great when you need:

Remove duplicate values
Keep only unique items
Check whether something already exists
Store unique IDs
Store tags
Store usernames
Store email addresses

When Should You Use an Array Instead?

Use an array if:

Duplicates matter
You need indexes
You need sorting or mapping
You care about item order and array methods

Arrays and Sets solve different problems.

Final Thoughts

Set is one of those JavaScript features that makes your code cleaner and easier to read.

If you come from Python, it will probably feel familiar.

If you're new to programming, think of it as a smart collection that automatically says:

"I already have this. I don't need another one."

Sometimes the simplest tools become your favorites.

DEV Community: PariSh KhAn

JavaScript Set Explained Like You're 10

Imagine a Toy Box

Creating Your First Set

Arrays Can Have Duplicates

Remove Duplicates Instantly

Convert It Back to an Array

Check If Something Exists

Remove Something

Remove Everything

Count Items

Loop Through a Set

A Real-Life Example

When Should You Use Set?

When Should You Use an Array Instead?

Final Thoughts