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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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 Set Reference
For a complete Set reference, go to our:
Complete JavaScript Set Reference.
The reference contains descriptions and examples of all Set properties and methods.