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10.9 JS Object Sets

A JavaScript Set is a collection of unique values.
Each value can only occur once in a Set.
A Set can hold 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 elements in a Set

How to Create a Set

You can create a JavaScript Set by:

Passing an Array to 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 1: JS Sets - The new Set() Method part 1

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

Create a Set and add literal values:

Example 2: JS Sets - The new Set() Method part 2

// Create a Set
const letters = new Set();

// Add Values to the Set
letters.add("a");
letters.add("b");
letters.add("c");

Create a Set and add variables:

Example 3: JS Sets - The new Set() Method part 3

// Create Variables
const a = "a";
const b = "b";
const c = "c";

// Create a Set
const letters = new Set();

// Add Variables to the Set
letters.add(a);
letters.add(b);
letters.add(c);

The add() Method

Example 4: JS Sets - The add() Method part 1

letters.add("d");
letters.add("e");

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

Example 5: JS Sets - The add() Method part 2

letters.add("a");
letters.add("b");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");

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

The forEach() Method

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

Example 6: JS Sets - The forEach() Method

// 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 containing all the values in a Set:

Example 7: JS Sets - The values() Method part 1

letters.values()   // Returns [object Set Iterator]

Now you can use the Iterator object to access the elements:

Example 8: JS Sets - The values() Method part 2

// Create an Iterator
const myIterator = letters.values();

// List all Values
let text = "";
for (const entry of myIterator) {
  text += entry;
}

The keys() Method

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

Example 9: JS Sets - The keys() Method

letters.keys()   // Returns [object Set Iterator]

The entries() Method

A Set has no keys.
entries() returns [value,value] pairs instead of [key,value] pairs.
This makes Sets compatible with Maps.

Example 10: JS Sets - The entries() Method

// Create an Iterator
const myIterator = letters.entries();

// List all Entries
let text = "";
for (const entry of myIterator) {
  text += entry;
}

Sets are Objects

For a Set, typeof returns object:

typeof letters;      // Returns object

Try it yourself

For a Set, instanceof Set returns true:

letters instanceof Set;  // Returns true

Try it yourself

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Module 10. JS Objects

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Example files created in this module:
JS Variables - Objects are Variables part 1 JS Variables - Objects are Variables part 2 JS Objects - Using an Object Literal part 1 JS Objects - Using an Object Literal part 2 JS Objects - Using an Object Literal part 3 JS Objects - Using the Keyword new JS Objects are Mutable JS Object Properties - Access a property with .property JS Object Properties - Access a property with ["property"] JS Object Properties - Looping object property values JS Object Properties - Add a new property to an existing object JS Object Properties - Deleting object properties part 1 JS Object Properties - Deleting object properties part 2 JS Objects - Access nested objects part 1 JS Objects - Access nested objects part2 JS Objects - Access nested objects part 3 JS Objects - Access nested objects part 4 JS Arrays - Nested JS Objects and Arrays JS Object Methods - this Keyword JS Objects - Creating and using an object method part 1 JS Objects - Creating and using an object method part 2 JS Objects - Adding a Method to an Object JS Objects - Using Built-In Methods JS Objects - Displaying a JavaScript object JS Objects - Display object properties JS Objects - Displaying the Object in a Loop JS Objects - Using Object.values() JS Objects - Using JSON.stringify() JS Objects - Stringify Dates JS Objects - Stringify Functions part 1 JS Objects - Stringify Functions part 2 JS Arrays - Stringify Arrays JS Getters and Setters - The get Keyword JS Getters and Setters - The set Keyword JS Object Methods part 1 JS Object Methods part 2 JS Getters and Setters - Data Quality part 1 JS Getters and Setters - Data Quality part 2 JS Getters and Setters - Object.defineProperty() JS Object Constructors JS Object Constructors - Add a Property to an Object JS Object Constructors - Adding a Method to an Object JS Object Constructors - Adding a Property to a Constructor part 1 JS Object Constructors - Adding a Property to a Constructor part 2 JS Object Constructors - Adding a Property to a Constructor part 3 JS Object Constructors - Adding a Method to a Constructor Did You Know? JS Objects - Using an object constructor JS Objects - Using the prototype Property part 1 JS Objects - Using the prototype Property part 2 JS Iterables - Iterate over a String JS Iterables - Iterating Over an Array JS Iterables - Home Made Iterable part 1 JS Iterables - Home Made Iterable part 2 JS Sets - The new Set() Method part 1 JS Sets - The new Set() Method part 2 JS Sets - The new Set() Method part 3 JS Sets - The add() Method part 1 JS Sets - The add() Method part 2 JS Sets - The forEach() Method JS Sets - The values() Method part 1 JS Sets - The values() Method part 2 JS Sets - The keys() Method JS Sets - The entries() Method JS Map Objects - new Map() JS Map Objects - Map.set() part 1 JS Map Objects - Map.set() part 2 JS Map Objects - Map.get() JS Map Objects - Map.size JS Map Objects - Map.delete() JS Map Objects - Map.clear() JS Maps using Map.has() JS Map Objects - Map typeof JS Map Objects - Map instanceof JS Map Objects - Using Map.forEach() JS Map Objects - Using Map.entries() JS Map Objects - Using Map.keys() JS Map Objects - Using Map.values() part 1 JS Map Objects - Using Map.values() part 2 JS Map Objects - Objects as Keys part 1 JS Map Objects - Objects as Keys part 2 JS Object - Changing a Property Value JS Objects - Listing All Properties JS Objects - Listing Enumerable Properties JS Objects - Adding a Property JS Objects - Adding Getters and Setters JS Objects - A Counter Example