Set.prototype.keys()

set.keys()

Returns: Set Iterator · Added in vES2015 · Updated March 13, 2026 · Map and Set

set iterator keys values iterable es2015 for...of

The keys() method returns a new Set Iterator object that contains the values for each element in the set, in insertion order. Introduced in ES2015, this method exists primarily for consistency with the Map object’s API.

Syntax

set.keys()

Return Value

A new Set Iterator object. The iterator yields the values (not keys, despite the method name) in the order they were inserted into the set.

Why Both keys() and values()?

Here’s the surprising part: Setkeys() is functionally identical to Setvalues(). They return exactly the same iterator.

This redundancy exists for API consistency with the Map object. When working with both Maps and Sets, it’s convenient to have a uniform interface:

Object	keys()	values()	entries()
Map	Returns keys	Returns values	Returns [key, value] pairs
Set	Returns values*	Returns values	Returns [value, value] pairs

*In a Set, there’s no meaningful distinction between keys and values—all elements are values. The keys() method exists purely for symmetry with Map.

Set vs Map: The Key Difference

While Mapkeys() returns the actual keys of a Map, Setkeys() returns the Set’s values (since Sets don’t have keys):

// Map - keys() returns actual keys
const map = new Map([['a', 1], ['b', 2]]);
console.log([...map.keys()]); // ['a', 'b']

// Set - keys() returns values (same as values())
const set = new Set(['a', 'b', 'c']);
console.log([...set.keys()]);  // ['a', 'b', 'c']
console.log([...set.values()]); // ['a', 'b', 'c'] - identical!

Examples

Basic iteration with for…of

The most common way to iterate over a Set’s values:

const colors = new Set(['red', 'green', 'blue']);

for (const color of colors.keys()) {
  console.log(color);
}
// Output:
// red
// green
// blue

Manual iteration with next()

Fine-grained control using the iterator protocol:

const numbers = new Set([10, 20, 30]);
const iterator = numbers.keys();

iterator.next(); // { value: 10, done: false }
iterator.next(); // { value: 20, done: false }
iterator.next(); // { value: 30, done: false }
iterator.next(); // { value: undefined, done: true }

Proving keys() is identical to values()

This example demonstrates that both methods return the same result:

const set = new Set([1, 2, 3]);

const keysIterator = set.keys();
const valuesIterator = set.values();

// They are the same object type
console.log(keysIterator[Symbol.toStringTag]); // 'Set Iterator'

// Same sequence of values
console.log(keysIterator.next().value);   // 1
console.log(valuesIterator.next().value); // 1

// Can be used interchangeably
console.log([...set.keys()]);   // [1, 2, 3]
console.log([...set.values()]); // [1, 2, 3]

When to Use

API consistency: Use keys() when you want uniform code between Map and Set handling
Explicit intent: Some developers prefer keys() to signal “iterating the set”
Modern iteration: Works seamlessly with for...of and spread operator

For most use cases, values() is clearer since it accurately describes what’s being returned.