What is JavaScript Set Methods?
JavaScript Sets are collections of unique values and they come equipped with several built-in methods to perform common operations. These methods make it easy to add, remove and check elements, among other tasks.
List of JavaScript Set Methods
- add()
- delete()
- has()
- clear()
- size (property, not a method)
- forEach()
- values()
- keys()
- entries()
1. add() Method
The add() method adds a new element to the Set. If the element already exists, it is ignored because Sets only store unique values.
Syntax:
set.add(value);
Example:
const mySet = new Set();
mySet.add('apple');
mySet.add('banana');
mySet.add('apple'); // Duplicate, ignored
console.log(mySet); // Output: Set(2) { 'apple', 'banana' }
2. delete() Method
The delete() method removes a specific element from the Set. It returns true if the element was removed and false if the element was not found.
Syntax:
set.delete(value);
Example:
const mySet = new Set(['apple', 'banana']);
console.log(mySet.delete('apple')); // Output: true
console.log(mySet.delete('orange')); // Output: false
console.log(mySet); // Output: Set(1) { 'banana' }
3. has() Method
The has() method checks if a specific element exists in the Set. It returns true if the element is found,and false otherwise.
Syntax:
set.has(value);
Example:
const mySet = new Set(['apple', 'banana']);
console.log(mySet.has('apple')); // Output: true
console.log(mySet.has('orange')); // Output: false
4. clear() Method
The clear() method removes all elements from the Set, leaving it empty.
Syntax:
set.clear();
Example:
const mySet = new Set(['apple', 'banana', 'orange']);
mySet.clear();
console.log(mySet); // Output: Set(0) {}
5. size Property
The size property returns the number of elements in a Set.
Syntax:
set.size;
Example:
const mySet = new Set(['apple', 'banana', 'orange']);
console.log(mySet.size); // Output: 3
6. forEach() Method
The forEach() method executes a provided function once for each element in the Set.
Syntax:
set.forEach(callbackFunction);
Example:
const mySet = new Set(['apple', 'banana', 'orange']);
mySet.forEach((value) => {
console.log(value);
});
// Output:
// apple
// banana
// orange
7. values() Method
The values() method returns an iterator object that contains all the values of the Set.
Syntax:
set.values();
Example:
const mySet = new Set(['apple', 'banana', 'orange']);
const values = mySet.values();
for (const value of values) {
console.log(value);
}
// Output:
// apple
// banana
// orange
8. keys() Method
The keys() method is identical to values() in Sets. It returns an iterator containing all the values (since Sets do not have keys).
Syntax:
set.keys();
Example:
const mySet = new Set(['apple', 'banana', 'orange']);
for (const key of mySet.keys()) {
console.log(key);
}
// Output:
// apple
// banana
// orange
9. entries() Method
The entries() method returns an iterator containing [value, value] pairs for each element in the Set. This format mimics the behavior of Map objects.
Syntax:
set.entries();
Example:
const mySet = new Set(['apple', 'banana', 'orange']);
for (const entry of mySet.entries()) {
console.log(entry);
}
// Output:
// [ 'apple', 'apple' ]
// [ 'banana', 'banana' ]
// [ 'orange', 'orange' ]
Practical Applications of Set Methods
Removing Duplicates from an Array
const duplicates = [1, 2, 2, 3, 4, 4];
const uniqueArray = [...new Set(duplicates)];
console.log(uniqueArray); // Output: [1, 2, 3, 4]
Checking Membership
const allowedUsers = new Set(['Alice', 'Bob', 'Charlie']);
console.log(allowedUsers.has('Alice')); // Output: true
console.log(allowedUsers.has('Eve')); // Output: false
Efficient Filtering
const setA = new Set([1, 2, 3, 4]);
const setB = new Set([3, 4, 5, 6]);
// Find common elements (intersection)
const intersection = new Set([...setA].filter(x => setB.has(x)));
console.log(intersection); // Output: Set(2) { 3, 4 }