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JS TutorialLesson #75

JavaScript Set Methods

Pass an array to the new Set() constructor:

Set Methods & Properties

new Set() add() clear() delete() entries()	forEach() has() keys() values() size

The new Set() Method

Pass an array to the new Set() constructor:

Example

Example Code

javascript

Try it Yourself

// Create a new Set

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

The add() Method

Example

Example Code

javascript

Try it Yourself

letters.add("d");

letters.add("e");

If you add equal elements, only the first will be saved:

Example

Example Code

javascript

Try it Yourself

letters.add("a");

letters.add("b");

letters.add("c");

letters.add("c");

letters.add("c");

letters.add("c");

letters.add("c");

letters.add("c");

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

Example Code

javascript

Try it Yourself

// Create a new Set

const mySet = new Set(["a","b","c"]);

// The number of elements are

mySet.size;

Listing Set Elements

You can list all Set elements (values) with a for..of loop:

Example

Example Code

javascript

Try it Yourself

// Create a Set

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

// List all Elements

let text = "";

for (const x of letters) {

  text += x;

}

The has() Method

The has() method returns true if a specified value exists in a set.

Example

Example Code

javascript

Try it Yourself

// Create a Set

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

// Does the Set contain "d"?

answer = letters.has("d");

The forEach() Method

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

Example

Example Code

javascript

Try it Yourself

// Create a Set

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

// List all entries

let text = "";

letters.forEach (function(value) {

  text += value;

})

The values() Method

The values() method returns an Iterator object with the values in a Set:

Example 1

Example Code

javascript

Try it Yourself

// 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;

}

Example 2

Example Code

javascript

Try it Yourself

// Create a Set

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

// List all Values

let text = "";

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

  text += entry;

}

The keys() Method

The keys() method returns an Iterator object with the values in a Set:

A Set has no keys, so keys() returns the same as values(). > This makes Sets compatible with Maps.

Example 1

Example Code

javascript

Try it Yourself

// 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;

}

Example 2

Example Code

javascript

Try it Yourself

// Create a Set

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

// List all Elements

let text = "";

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

  text += x;

}

The entries() Method

The entries() method returns an Iterator with [value,value] pairs from a Set.

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

Example Code

javascript

Try it Yourself

// 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;

}

Example 2

Example Code

javascript

Try it Yourself

// Create a Set

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

// List all Entries

let text = "";

for (const entry of letters.entries()) {

  text += entry;

}

JavaScript syntax and algorithm demonstration.

// Create a Set

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



// Does the Set contain "d"?

answer = letters.has("d");

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