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JS References

JavaScript Objects


JavaScript Set Methods

The new Set() Method

Pass an array to the new Set() constructor:

Example

// Create a new Set
const letters = new Set(["a","b","c"]);
Try it Yourself »

The add() Method

Example

letters.add("d");
letters.add("e");
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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");
Try it Yourself »

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;
}
Try it Yourself »

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;
})
Try it Yourself »

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;
}
Try it Yourself »

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;
}
Try it Yourself »

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;
}
Try it Yourself »

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;
}
Try it Yourself »

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;
}
Try it Yourself »

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 »



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