javascript 单身创造设计模式

Posted 2021-05-03

## Real world example
There can only be one president of a country at a time. The same president has to be brought to action, whenever duty calls. President here is singleton.

## In plain words
Ensures that only one object of a particular class is ever created.

## Wikipedia says
In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system.

Singleton pattern is actually considered an anti-pattern and overuse of it should be avoided. It is not necessarily bad and could have some valid use-cases but should be used with caution because it introduces a global state in your application and change to it in one place could affect in the other areas and it could become pretty difficult to debug. The other bad thing about them is it makes your code tightly coupled plus it mocking the singleton could be difficult.

const president = (function(){
    const presidentsPrivateInformation = 'Super private'

    const name = 'Turd Sandwich'

    const getName = () => name

    return {
        getName
    }
}())


// IMPLEMENTATION
president.getName() // Outputs 'Turd Sandwich'
president.name // Outputs undefined
president.presidentsPrivateInformation // Outputs undefined