Check if a Set contains a Value using JavaScript


Borislav Hadzhiev

Last updated: Oct 27, 2021


Photo from Unsplash

Check if a Set contains a Value in JavaScript #

Use the has() method to check if a Set contains a value, e.g. set.has(1). The has method returns true if the value is contained in the Set, otherwise false is returned.

const set1 = new Set(['one', 'two', 'three']); console.log(set1.has('one')); // 👉️ true console.log(set1.has('four')); // 👉️ false

The only parameter the Set.has method takes is the value we want to test for presence in the Set.

The has method returns a boolean result:

  • true if the value is contained in the Set
  • false if the value is not in the Set

Here are some more examples.

const set1 = new Set(); const obj = {country: 'Chile'}; set1.add(obj); console.log(set1.has(obj)); // 👉️ true const arr = ['one', 'two']; set1.add(arr); console.log(set1.has(arr)); // 👉️ true // 👇️ false because they reference // different locations in memory console.log(set1.has(['one', 'two'])); set1.delete(arr); console.log(set1.has(arr)); // 👉️ false

The has method works even with object and arrays, as long as they have the same reference.

The has method does not check for equality of the values of the object or array, instead it checks if they reference the same location in memory.

const obj = {}; console.log(obj === obj); // 👉️ true console.log({} === {}); // 👉️ false

Further Reading #

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.
book cover
You can use the search field on my Home Page to filter through all of my articles.