Check if a Map or a Set is Empty in JavaScript

# Table of Contents

1. Check if a Map is Empty in JavaScript
2. Check if a Set is Empty in JavaScript

# Check if a Map is Empty in JavaScript

Use the size property to check if a Map is empty, e.g. map.size === 0. The size property returns the number of elements in the Map.

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

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const map1 = new Map();
console.log(map1.size); // 👉️ 0

if (map1.size === 0) {
  // 👇️ this runs
  console.log('✅ map is empty');
} else {
  console.log('⛔️ map is not empty');
}

We used the Map.size property on the Map to check if it's empty.

The property returns the number of elements the Map stores.

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const map2 = new Map();
map2.set('country', 'Chile');
console.log(map2.size); // 👉️ 1

The property is very similar to an array's length property, however, it is read-only and cannot be changed.

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const map = new Map();
map.set('country', 'Chile');
console.log(map.size); // 👉️ 1

// ⛔️ TypeError: Cannot set property size of #<Map> which has only a getter
map.size = 5;

Even though we attempted to set the size property on the Map, we were unable to.

This behavior is different when working with arrays.

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const arr = ['a', 'b', 'c'];
console.log(arr.length); // 👉️ 3

arr.length = 1;

console.log(arr.length); // 👉️ 1
console.log(arr); // 👉️ ['a']

We set the array's length to 1 which automatically removed the last 2 elements from the array.

Map objects also have keys() and values() methods.

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const map1 = new Map();

map1.set('name', 'bobby hadz');
map1.set('country', ['Chile', 'ab']);
map1.set('age', 30);

const keys = [...map1.keys()];
console.log(keys.length); // 👉️ 3
console.log(keys.length === 0); // 👉️ false

const values = [...map1.values()];
console.log(values.length); // 👉️ 3
console.log(values.length === 0); // 👉️ false

The Map.keys method returns an iterator object that contains the keys of the Map.

The Map.values() method returns an iterator object containing the values for each element in the Map.

We used the spread syntax (...) to convert the iterator objects to an array and accessed the length property on the arrays to check if the Map is empty.

However, using the size property on the Map object is more convenient and direct.

If you need to empty a Map object, use the Map.clear() method.

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const map1 = new Map();

map1.set('name', 'bobby hadz');
map1.set('country', ['Chile', 'ab']);
map1.set('age', 30);

console.log(map1.size); // 👉️ 3

map1.clear();

console.log(map1.size); // 👉️ 0
console.log(map1); // 👉️ Map(0) {}

The Map.clear() method removes all elements from a Map object.

If you have to check if a Map object is empty often, define a reusable function.

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function mapIsEmpty(map) {
  return map.size === 0;
}

// 👇️ false
console.log(
  mapIsEmpty(
    new Map([
      ['name', 'bobby'],
      ['age', 30],
    ]),
  ),
);

// 👇️ true
console.log(mapIsEmpty(new Map()));

The mapIsEmpty() function takes a Map object as a parameter and returns true if it is empty and false otherwise.

# Check if a Set is Empty in JavaScript

Use the size property to check if a Set is empty, e.g. set.size === 0. The size property returns the number of elements in the Set.

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

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const set1 = new Set();
console.log(set1.size); // 👉️ 0

if (set1.size === 0) {
  // 👇️ this runs
  console.log('✅ Set is empty');
} else {
  console.log('⛔️ Set is NOT empty');
}

We used the Set.size property to check if a Set is empty.

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const set2 = new Set(['a', 'b']);
console.log(set2.size); // 👉️ 2

The property is similar to an array's length property, however, it is read-only and cannot be changed.

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const set1 = new Set(['bobby', 'hadz', 'com']);
console.log(set1.size); // 👉️ 3

// ⛔️ TypeError: Cannot set property size of #<Set> which has only a getter
set1.size = 1;

We attempted to change the size property on the Set, however, we were unable to.

This is different when working with arrays, where the value of the length property can be set by the user.

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const arr = ['bobby', 'hadz', 'com'];
console.log(arr.length); // 👉️ 3

arr.length = 1;

console.log(arr.length); // 👉️ 1
console.log(arr); // 👉️ [ 'bobby' ]

As opposed to a Set's size property we were able to set the array's length property and change the array's contents.

If you need to empty a Set object, use the Set.clear() method.

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const set1 = new Set(['bobby', 'hadz', 'com']);
console.log(set1.size); // 👉️ 3

set1.clear();

console.log(set1.size); // 👉️ 0
console.log(set1); // 👉️ Set(0) {}

The Set.clear() method removes all elements from a Set object.

If you have to check if a Set object is empty often, define a reusable function.

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function setIsEmpty(set) {
  return set.size === 0;
}

// 👇️ false
console.log(setIsEmpty(new Set(['bobby', 'hadz'])));

// 👇️ true
console.log(setIsEmpty(new Set()));

The setIsEmpty function takes a Set object as a parameter and returns true if it is empty and false otherwise.

# Additional Resources

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

• Check if an Object is of type Map or Set in JavaScript
• How to convert an Array to a Map in JavaScript
• Convert a Map to an Array of Objects in JavaScript
• How to Convert a Map to JSON in JavaScript
• Convert a Map to an Object in JavaScript
• Convert Map Keys and Values to an Array in JavaScript
• How to Clear an Object in JavaScript