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A JavaScript Set is a collection of unique values
| 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 |
You can create a JavaScript Set by:
new Set()add() to add valuesadd() to add variablesPass an Array to the new Set() constructor:
// Create a Set
const letters = new Set(["a","b","c"]);
Create a Set and add literal values:
// 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:
// 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);
letters.add("d");
letters.add("e");
If you add equal elements, only the first will be saved:
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 forEach() method invokes a function for each Set element:
// Create a Set
const letters = new Set(["a","b","c"]);
// List all entries
let text = "";
letters.forEach (function(value) {
text += value;
})
The values() method returns an Iterator object containing all the values in a Set:
letters.values() // Returns [object Set Iterator]
Now you can use the Iterator object to access the elements:
// Create an Iterator
const myIterator = letters.values();
// List all Values
let text = "";
for (const entry of myIterator) {
text += entry;
}
A Set has no keys.
keys() returns the same as
values().
This makes Sets compatible with Maps.
letters.keys() // Returns [object Set Iterator]
A Set has no keys.
entries() returns [value,value] pairs
instead of [key,value] pairs.
This makes Sets compatible with Maps:
// Create an Iterator
const myIterator = letters.entries();
// List all Entries
let text = "";
for (const entry of myIterator) {
text += entry;
}
For a Set, typeof returns object:
typeof letters; // Returns object
For a Set, instanceof Set returns true:
letters instanceof Set; // Returns true