How to get the Union of Two Sets in JavaScript

Get the Union of Two Sets in JavaScript #

To get a union of two Sets, use the spread syntax (...) to unpack the values of the Sets into an array and pass the result to the Set() constructor, e.g. new Set([...set1, ...set2]). The new Set will contain the union of the other two.

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const set1 = new Set(['a', 'b', 'c']);
const set2 = new Set(['a', 'b', 'd']);

const union = new Set([...set1, ...set2]);
console.log(union); // 👉️ {'a', 'b', 'c', 'd'}

We used the spread syntax (...) to unpack the values from the two Set objects into an array.

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const set1 = new Set(['a', 'b', 'c']);
const set2 = new Set(['a', 'b', 'd']);

const arr = [...set1, ...set2];

console.log(arr); // 👉️ ['a', 'b', 'c' ,'a', 'b', 'd']

The array stores duplicate values as opposed to a Set. Once the array is passed to the Set() constructor, all of the duplicates are ignored.

The Set() constructor takes an iterable object as a parameter, so an array is perfect.

Get a Union of Two Sets using for of loop #

To get a union of two Sets, pass the first Set to the Set() constructor to create a third Set. Then use the for...of loop to iterate over the second Set and add each element to the newly created Set. The new Set will contain a union of the other two Sets.

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function getUnion(setA, setB) {
  const union = new Set(setA);

  for (const element of setB) {
    union.add(element);
  }

  return union;
}

const set1 = new Set(['a', 'b', 'c']);
const set2 = new Set(['a', 'b', 'd']);

console.log(getUnion(set1, set2)); // 👉️ {'a', 'b', 'c', 'd'}

We created a reusable function which returns the union of two Sets.

The first step is to create a new Set from the first Set.

Then, we used the for...of loop to iterate over the second Set and add its values to the new Set.

Further Reading #

• Get the Intersection of two Sets using JavaScript
• Replace all Commas in a String using JavaScript