JavaScript Set Methods
Basic Set Methods
new Set()add()
clear()
delete()
entries()
forEach()
has()
keys()
values()
Set Properties
The new Set() Method
Pass an array to the new Set() constructor:
The add() Method
If you add equal elements, only the first will be saved:
Example
letters.add("a");
letters.add("b");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
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Note
The primary feature of Set objects is that they only store unique values.
If an attempt is made to add an element that already exists in the set, the add() method will have no effect,
and the set will remain unchanged.
The size Property
Example
// Create a new Set
const mySet = new Set(["a","b","c"]);
// The number of elements are
mySet.size;
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Listing Set Elements
You can list all Set elements (values) with a for..of loop:
Example
// Create a Set
const letters = new Set(["a","b","c"]);
// List all Elements
let text = "";
for (const x of letters) {
text += x;
}
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The has() Method
The has() method returns true if a specified value exists in a set.
Example
// Create a Set
const letters = new Set(["a","b","c"]);
// Does the Set contain "d"?
answer = letters.has("d");
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The forEach() Method
The forEach() method invokes a function for each Set element:
Example
// Create a Set
const letters = new Set(["a","b","c"]);
// List all entries
let text = "";
letters.forEach (function(value) {
text += value;
})
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The values() Method
The values() method returns an Iterator object with the values in a Set:
Example 1
// Create a Set
const letters = new Set(["a","b","c"]);
// Get all Values
const myIterator = letters.values();
// List all Values
let text = "";
for (const entry of myIterator) {
text += entry;
}
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Example 2
// Create a Set
const letters = new Set(["a","b","c"]);
// List all Values
let text = "";
for (const entry of letters.values()) {
text += entry;
}
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The keys() Method
The keys() method returns an Iterator object with the values in a Set:
Note
A Set has no keys, so keys() returns the same as values().
This makes Sets compatible with Maps.
Example 1
// Create a Set
const letters = new Set(["a","b","c"]);
// Create an Iterator
const myIterator = letters.keys();
// List all Elements
let text = "";
for (const x of myIterator) {
text += x;
}
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Example 2
// Create a Set
const letters = new Set(["a","b","c"]);
// List all Elements
let text = "";
for (const x of letters.keys()) {
text += x;
}
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The entries() Method
The entries() method returns an Iterator with [value,value] pairs from a Set.
Note
The entries() method is supposed to return a [key,value] pair from an object.
A Set has no keys, so the entries() method returns [value,value].
This makes Sets compatible with Maps.
Example 1
// Create a Set
const letters = new Set(["a","b","c"]);
// Get all Entries
const myIterator = letters.entries();
// List all Entries
let text = "";
for (const entry of myIterator) {
text += entry;
}
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Example 2
// Create a Set
const letters = new Set(["a","b","c"]);
// List all Entries
let text = "";
for (const entry of letters.entries()) {
text += entry;
}
Try it Yourself »
Complete JavaScript Reference
For a complete reference to all JavaScript properties and methods, with full descriptions and many examples, go to:
W3Schools' Full JavaScript Reference.
The reference inludes all JavaScript updates from 1999 to 2025.
