Singleton Pattern
CreationalWhat is it?
Ensures a class has only one instance and provides a global point of access to it. In JavaScript, this is often implemented using closures or modules to maintain a single instance.
Why use it?
The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. This is useful when exactly one object is needed to coordinate actions across the system. For example, you might use a Singleton for managing a database connection or a configuration object, ensuring that all parts of your application use the same, consistent resource.
Code Example
typescript
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
// Singleton Pattern Example
class Database {
constructor() {
if (Database.instance) {
return Database.instance;
}
this.connection = this.createConnection();
Database.instance = this;
}
createConnection() {
return {
host: 'localhost',
port: 5432,
connected: true
};
}
query(sql) {
console.log(`Executing query: ${sql}`);
return 'Query results';
}
}
// Usage
const db1 = new Database();
const db2 = new Database();
console.log(db1 === db2); // true - same instance
// Alternative implementation using closure
const DatabaseSingleton = (() => {
let instance;
function createInstance() {
return {
connection: { host: 'localhost', port: 5432 },
query(sql) {
console.log(`Executing: ${sql}`);
}
};
}
return {
getInstance() {
if (!instance) {
instance = createInstance();
}
return instance;
}
};
})();
const db3 = DatabaseSingleton.getInstance();
const db4 = DatabaseSingleton.getInstance();
console.log(db3 === db4); // trueQuick Facts
- Category
- Creational
- Common Use Cases
- Object creation, instance management