Set.prototype.add()
Adds a value to a Set if it is not already present.
Syntax
set.add(value)
Returns
Set — The `Set` itself, allowing chained calls.
Examples
const s = new Set();
s.add(1).add(2).add(2);
console.log([...s]);
Output
[ 1, 2 ]
const s = new Set();
s.add(NaN);
s.add(NaN);
console.log(s.size);
Output
1
Notes
- Duplicate values are ignored; uniqueness uses SameValueZero so `NaN`
is treated as equal to `NaN`.
- Returns the set, enabling chained `add()` calls.
Browser & runtime support
| Environment | Since version |
|---|---|
| chrome | 38 |
| firefox | 13 |
| safari | 8 |
| edge | 12 |
| node | 0.12 |