{{JSRef}}
The Set object lets you store unique values of any type, whether {{Glossary("Primitive", "primitive values")}} or object references.
Syntax
new Set([iterable]);
Parameters
- iterable
- If an iterable object is passed, all of its elements will be added to the new Set. null is treated as undefined.
Description
Set objects are collections of values, you can iterate its elements in insertion order. A value in the Set may only occur once; it is unique in the Set's collection.
Value equality
Because each value in the Set has to be unique, the value equality will be checked and is not based on the same algorithm as the one used in the === operator. Specifically, for Sets, +0 (which is strictly equal to -0) and -0 are different values. However, this has been changed in the latest ECMAScript 6 specification. Starting with Gecko 29.0 {{geckoRelease("29")}} ({{bug("952870")}}) and a recent nightly Chrome, +0 and -0 are treated as the same value in Set objects. Also, NaN and undefined can also be stored in a Set. NaN is considered the same as NaN (even though NaN !== NaN).
Properties
Set.length- The value of the
lengthproperty is 0. - {{jsxref("Set.@@species", "get Set[@@species]")}}
- The constructor function that is used to create derived objects.
- {{jsxref("Set.prototype")}}
- Represents the prototype for the
Setconstructor. Allows the addition of properties to allSetobjects.
Set instances
All Set instances inherit from {{jsxref("Set.prototype")}}.
Properties
{{page('en-US/Web/JavaScript/Reference/Global_Objects/Set/prototype','Properties')}}
Methods
{{page('en-US/Web/JavaScript/Reference/Global_Objects/Set/prototype','Methods')}}
Examples
Using the Set object
var mySet = new Set();
mySet.add(1);
mySet.add(5);
mySet.add("some text");
var o = {a: 1, b: 2};
mySet.add(o);
mySet.has(1); // true
mySet.has(3); // false, 3 has not been added to the set
mySet.has(5); // true
mySet.has(Math.sqrt(25)); // true
mySet.has("Some Text".toLowerCase()); // true
mySet.has(o); // true
mySet.size; // 4
mySet.delete(5); // removes 5 from the set
mySet.has(5); // false, 5 has been removed
mySet.size; // 3, we just removed one value
Iterating Sets
// iterate over items in set // logs the items in the order: 1, "some text" for (let item of mySet) console.log(item); // logs the items in the order: 1, "some text" for (let item of mySet.keys()) console.log(item); // logs the items in the order: 1, "some text" for (let item of mySet.values()) console.log(item); // logs the items in the order: 1, "some text" //(key and value are the same here) for (let [key, value] of mySet.entries()) console.log(key); // convert set to plain Array (with Array comprehensions) var myArr = [v for (v of mySet)]; // [1, "some text"] // Alternative (with Array.from) var myArr = Array.from(mySet); // [1, "some text"] // the following will also work if run in an HTML document mySet.add(document.body); mySet.has(document.querySelector("body")); // true // converting between Set and Array mySet2 = new Set([1,2,3,4]); mySet2.size; // 4 [...mySet2]; // [1,2,3,4] // intersect can be simulated via var intersection = new Set([...set1].filter(x => set2.has(x))); // difference can be simulated via var difference = new Set([...set1].filter(x => !set2.has(x))); // Iterate set entries with forEach mySet.forEach(function(value) { console.log(value); }); // 1 // 2 // 3 // 4
Relation with Array objects
var myArray = ["value1", "value2", "value3"];
// Use the regular Set constructor to transform an Array into a Set
var mySet = new Set(myArray);
mySet.has("value1"); // returns true
// Use the spread operator to transform a set into an Array.
console.log(uneval([...mySet])); // Will show you exactly the same Array as myArray
Specifications
| Specification | Status | Comment |
|---|---|---|
| {{SpecName('ES6', '#sec-set-objects', 'Set')}} | {{Spec2('ES6')}} | Initial definition. |
| {{SpecName('ESDraft', '#sec-set-objects', 'Set')}} | {{Spec2('ESDraft')}} |
Browser compatibility
{{CompatibilityTable}}
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support |
{{ CompatChrome(38) }} [1] |
{{ CompatGeckoDesktop("13") }} | {{ CompatIE("11") }} | 25 | 7.1 |
Constructor argument: new Set(iterable) |
{{ CompatChrome(38) }} | {{ CompatGeckoDesktop("13") }} | {{CompatNo}} | 25 | {{CompatNo}} |
| iterable | {{ CompatChrome(38) }} | {{ CompatGeckoDesktop("17") }} | {{CompatNo}} | 25 | 7.1 |
Set.clear() |
{{ CompatChrome(38) }} | {{CompatGeckoDesktop("19")}} | {{ CompatIE("11") }} | 25 | 7.1 |
Set.keys(), Set.values(), Set.entries() |
{{ CompatChrome(38) }} | {{CompatGeckoDesktop("24")}} | {{CompatNo}} | 25 | 7.1 |
Set.forEach() |
{{ CompatChrome(38) }} | {{CompatGeckoDesktop("25")}} | {{ CompatIE("11") }} | 25 | 7.1 |
| Value equality for -0 and 0 | {{ CompatChrome(38) }} | {{CompatGeckoDesktop("29")}} | {{CompatNo}} | 25 | {{CompatNo}} |
Constructor argument: new Set(null) |
{{CompatVersionUnknown}} | {{CompatGeckoDesktop("37")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
Monkey-patched add() in Constructor |
{{CompatVersionUnknown}} | {{CompatGeckoDesktop("37")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
Set[@@species] |
{{CompatUnknown}} | {{CompatGeckoDesktop("41")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
Set() without new throws |
{{CompatUnknown}} | {{CompatGeckoDesktop("42")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Basic support | {{CompatNo}} | {{CompatChrome(38)}} [1] | {{ CompatGeckoMobile("13") }} | {{CompatNo}} | {{CompatNo}} | 8 |
Constructor argument: new Set(iterable) |
{{CompatNo}} | {{CompatChrome(38)}} | {{ CompatGeckoMobile("13") }} | {{CompatNo}} | {{CompatNo}} | {{CompatNo}} |
| iterable | {{CompatNo}} | {{CompatNo}} | {{ CompatGeckoMobile("17") }} | {{CompatNo}} | {{CompatNo}} | 8 |
Set.clear() |
{{CompatNo}} | {{ CompatChrome(38) }} | {{CompatGeckoMobile("19")}} | {{CompatNo}} | {{CompatNo}} | 8 |
Set.keys(), Set.values(), Set.entries() |
{{CompatNo}} | {{ CompatChrome(38) }} | {{CompatGeckoMobile("24")}} | {{CompatNo}} | {{CompatNo}} | 8 |
Set.forEach() |
{{CompatNo}} | {{ CompatChrome(38) }} | {{CompatGeckoMobile("25")}} | {{CompatNo}} | {{CompatNo}} | 8 |
| Value equality for -0 and 0 | {{CompatNo}} | {{ CompatChrome(38) }} | {{CompatGeckoMobile("29")}} | {{CompatNo}} | {{CompatNo}} | {{CompatNo}} |
Constructor argument: new Set(null) |
{{CompatUnknown}} | {{CompatVersionUnknown}} | {{CompatGeckoMobile("37")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
Monkey-patched add() in Constructor |
{{CompatUnknown}} | {{CompatVersionUnknown}} | {{CompatGeckoMobile("37")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
Set[@@species] |
{{CompatUnknown}} | {{CompatUnknown}} | {{CompatGeckoMobile("41")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
Set() without new throws |
{{CompatUnknown}} | {{CompatUnknown}} | {{CompatGeckoMobile("42")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
[1] The feature was available behind a preference from Chrome 31. In chrome://flags, activate the entry “Enable Experimental JavaScript”.
See also
- {{jsxref("Map")}}
- {{jsxref("WeakMap")}}
- {{jsxref("WeakSet")}}