Creating and Using Sets

Sets provide intuitive methods for managing collections of unique values. Understanding how to create and manipulate Sets is essential for effective usage.

Creating Sets

Method	Description	Example
Empty Set	Create with no values	new Set()
From iterable	Pass array or any iterable	new Set([1,2,3])
From another Set	Clone existing Set	new Set(existingSet)
From string	Characters become elements	new Set('hello')

Basic Usage Pattern

// Create
const set = new Set();

// Add values
set.add(value);

// Check existence
const exists = set.has(value);

// Delete value
set.delete(value);

// Clear all
set.clear();

Key Points

• add() returns the Set object (allows chaining).
• add() does nothing if value already exists.
• has() returns boolean in O(1) time.
• delete() returns true if value existed.
• clear() removes all values.

Example Code

// Different ways to create Sets

// 1. Empty Set
const emptySet = new Set();
console.log(emptySet.size); // 0

// 2. From array
const colors = new Set(["red", "green", "blue", "red"]);
console.log(colors); // Set {'red', 'green', 'blue'}
console.log(colors.size); // 3

// 3. From another Set (cloning)
const original = new Set([1, 2, 3]);
const clone = new Set(original);
console.log(clone); // Set {1, 2, 3}

// 4. From generator
function* generateNumbers() {
  yield 1;
  yield 2;
  yield 2;
  yield 3;
}
const genSet = new Set(generateNumbers());
console.log(genSet); // Set {1, 2, 3}

// 5. From NodeList (DOM)
// const divs = new Set(document.querySelectorAll('div'));

// Chaining add() calls
const chainSet = new Set()
  .add("apple")
  .add("banana")
  .add("apple") // Duplicate, ignored
  .add("orange");

console.log(chainSet); // Set {'apple', 'banana', 'orange'}

// has() method
const fruits = new Set(["apple", "banana", "orange"]);
console.log(fruits.has("apple")); // true
console.log(fruits.has("grape")); // false

// delete() method
console.log(fruits.delete("banana")); // true
console.log(fruits.delete("banana")); // false (already deleted)
console.log(fruits.size); // 2

// clear() method
const tempSet = new Set([1, 2, 3]);
console.log(tempSet.size); // 3
tempSet.clear();
console.log(tempSet.size); // 0

// Practical: Unique ID tracker
class UniqueIDTracker {
  constructor() {
    this.ids = new Set();
  }

  addID(id) {
    if (this.ids.has(id)) {
      console.log(`ID ${id} already exists`);
      return false;
    }
    this.ids.add(id);
    console.log(`ID ${id} added`);
    return true;
  }

  hasID(id) {
    return this.ids.has(id);
  }

  removeID(id) {
    return this.ids.delete(id);
  }

  get count() {
    return this.ids.size;
  }

  clear() {
    this.ids.clear();
  }
}

const tracker = new UniqueIDTracker();
tracker.addID("usr-001"); // ID usr-001 added
tracker.addID("usr-002"); // ID usr-002 added
tracker.addID("usr-001"); // ID usr-001 already exists
console.log(tracker.hasID("usr-002")); // true
console.log(tracker.count); // 2
tracker.removeID("usr-002");
console.log(tracker.count); // 1