Set.prototype.add()
 The add() method appends a new element with a specified value to the end of a Set object. 
Syntax
add(value)
Parameters
- value
-  The value of the element to add to the Setobject.
Return value
The Set object with added value.
Examples
Using the add() method
var mySet = new Set(); mySet.add(1); mySet.add(5).add('some text'); // chainable console.log(mySet); // Set [1, 5, "some text"]
Specifications
Browser compatibility
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
| add | 38 | 12 | 13 | 11 Returns 'undefined' instead of the 'Set' object. | 25 | 8 | 38 | 38 | 14 | 25 | 8 | 3.0 | 
See also
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    https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/add