How to get the Length of a Set in JavaScript

# Get the Length of a Set in JavaScript

Use the size property to get the length of a Set, e.g. mySet.size. The size property returns the number of values in the Set object.

When accessed on an empty Set, the size property returns 0.

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const set = new Set(['a', 'b', 'c']);

console.log(set.size); // 👉️ 3

set.add('d');
set.add('e');

console.log(set.size); // 👉️ 5

We used the Set.size property to get the number of elements in the Set object.

As opposed to the array's length property, the size property is read-only and can't be changed by the user.

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const set = new Set(['a', 'b', 'c']);

console.log(set.size); // 👉️ 3

set.size = 10;

console.log(set.size); // 👉️ 3

Even though we tried to update the size of the Set, we were unable to.

This is not the case when using the array's length property.

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const arr = ['a', 'b', 'c'];

console.log(arr.length); // 👉️ 3

arr.length = 10;

console.log(arr.length); // 👉️ 10

The code sample shows that we can update the array's length and contents by using its length property.

As expected, the size of the Set object is updated when:

• you add an element to the Set
• you remove an element from the Set
• you use the Set.clear() method to remove all elements from the Set

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const set = new Set();

console.log(set.size); // 👉️ 0

// ✅ add elements to the Set
set.add('bobby');
set.add('hadz');

console.log(set.size); // 👉️ 2

// ✅ delete an element from the set
set.delete('bobby');

console.log(set.size); // 👉️ 1

// ✅ clear the set object
set.clear();

console.log(set.size); // 👉️ 0

We used the Set.add() method to add 2 elements to the Set object.

Accessing the size property on the Set returns 2 at this point.

We used the Set.delete() method to remove an element from the Set.

Accessing the size property returned 1 after removing the element.

Finally, we used the Set.clear() method to remove all elements from the Set, so the size property returned 0.

# Get the length of a Set using Set.forEach()

You can also use the Set.forEach() method to get the length of a Set.

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const set = new Set();

console.log(set.size); // 👉️ 0

set.add('bobby');
set.add('hadz');

let length = 0;

set.forEach(_element => {
  length += 1;
});

console.log(length); // 👉️ 2

We declared a length variable and used the Set.forEach() method to iterate over a Set.

On each iteration, we increment the length variable by 1 to get the total length of the Set.

Note that the length variable has to be declared using let because variables declared using const cannot be reassigned.

However, most of the time using the forEach() method is not necessary because the Set.size property does exactly what we need and gets automatically updated.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• How to Clear an Object in JavaScript
• Convert a Map to an Object in JavaScript
• Convert Map Keys and Values to an Array in JavaScript
• Check if a Map or a Set is Empty in JavaScript