Object Sets

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Object Sets

A JavaScript Set is a collection of unique values.

Each value can only occur once in a Set.

A Set can store any value of any data type.

Set Methods

Method

Description

new Set()

Creates a new Set

add()

Adds a new element to the Set

delete()

Removes an element from a Set

has()

Returns true if a value exists

clear()

Removes all elements from a Set

forEach()

Invokes a callback for each element

values()

Returns an Iterator with all the values in a Set

keys()

Same as values()

entries()

Returns an Iterator with the [value, value] pairs from a Set

Property

Description

size

Returns the number of elements in a Set

How to Create a Set

Create a JavaScript Set by:

  • Passing an Array to a new Set().
  • Create a new Set and use add() to add values.
  • Create a new Set and use add() to add variables.

The new Set() Method

Pass an Array to the new Set() constructor:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Create a Set from an Array:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set([“a”,”b”,”c”]);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.size;

</script>

</body>

</html>

Output

JavaScript Sets

Create a Set from an Array:

Create a Set and add literal values:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Add values to a Set:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set();

// Add Values to the Set

letters.add(“a”);

letters.add(“b”);

letters.add(“c”);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.size;

</script>

</body>

</html>

Output

JavaScript Sets

Add values to a Set:

3

Create a Set and add variables:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Add variables to a Set:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set();

// Create Variables

const a = “a”;

const b = “b”;

const c = “c”;

// Add the Variables to the Set

letters.add(a);

letters.add(b);

letters.add(c);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.size;

</script>

</body>

</html>

Output

JavaScript Sets

Add variables to a Set:

3

The add() Method

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Adding new elements to a Set:</p>

<p id=”demo”></p>

<script>

// Create a new Set

const letters = new Set([“a”,”b”,”c”]);

// Add a new Element

letters.add(“d”);

letters.add(“e”);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.size;

</script>

</body>

</html>

Output

JavaScript Sets

Adding new elements to a Set:

5

Adding equal elements, only the first will be saved:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Adding equal elements to a Set:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set();

// Add values to the Set

letters.add(“a”);

letters.add(“b”);

letters.add(“c”);

letters.add(“c”);

letters.add(“c”);

letters.add(“c”);

letters.add(“c”);

letters.add(“c”);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.size;

</script>

</body>

</html>

Output

JavaScript Sets

Adding equal elements to a Set:

3

The forEach() Method

The forEach() method invokes a function for each Set element:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>forEach() calls a function for each element:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set([“a”,”b”,”c”]);

// List all Elements

let text = “”;

letters.forEach (function(value) {

  text += value + “<br>”;

})

document.getElementById(“demo”).innerHTML = text;

</script>

</body>

</html>

Output

JavaScript Sets

forEach() calls a function for each element:

a
b
c

The values() Method

The values() method returns an Iterator object consisting of all the values in a Set:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Set.values() returns a Set Iterator:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set([“a”,”b”,”c”]);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.values();

</script>

</body>

</html>

Output

JavaScript Sets

Set.values() returns a Set Iterator:

[object Set Iterator]

Use the Iterator object to access the elements:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Iterating Set values:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set([“a”,”b”,”c”]);

// List all Elements

let text = “”;

for (const x of letters.values()) {

  text += x + “<br>”;

}

document.getElementById(“demo”).innerHTML = text;

</script>

</body>

</html>

Output

JavaScript Sets

Iterating Set values:

a
b
c

The keys() Method

A Set has no keys.

keys() returns the same as values().

This makes Sets compatible with Maps.

Example

<html>

<body>

<h2>JavaScript Sets</h2>

<p>Set.keys() returns a Set Iterator:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set([“a”,”b”,”c”]);

// Display set.size

document.getElementById(“demo”).innerHTML = letters.keys();

</script>

</body>

</html>

Output

JavaScript Sets

Set.keys() returns a Set Iterator:

[object Set Iterator]

The entries() Method

A Set has no keys.

keys() returns the same as values().

This makes Sets compatible with Maps.

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>entries() Returns an Iterator with [value,value] pairs from a Set:</p>

<p id=”demo”></p>

<script>

// Create a Set

const letters = new Set([“a”,”b”,”c”]);

// List all entries

const iterator = letters.entries();

let text = “”;

for (const entry of iterator) {

  text += entry + “<br>”;

}

document.getElementById(“demo”).innerHTML = text;

</script>

</body>

</html>

Output

JavaScript Sets

entries() Returns an Iterator with [value,value] pairs from a Set:

a,a
b.b
c,c

Sets are Objects

For a Set, typeof returns object:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets Objects</h2>

<p>The type of operator returns object:</p>

<p id=”demo”></p>

<script>

// Create a new Set

const letters = new Set([“a”,”b”,”c”]);

// Display typeof

document.getElementById(“demo”).innerHTML = typeof letters;

</script>

</body>

Output

JavaScript Sets Objects

The type of operator returns object:

object

For a Set, an instance of Set returns true:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Sets</h2>

<p>The instance of operator returns true:</p>

<p id=”demo”></p>

<script>

// Create a new Set

const letters = new Set([“a”,”b”,”c”]);

// Display typeof

document.getElementById(“demo”).innerHTML = letters instanceof Set;

</script>

</body>

</html>

Output

JavaScript Sets

The instance of operator returns true:

true


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