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JavaScriptのSingleton パターン

Last updated at Posted at 2022-05-29

Classバージョン

export class Singleton {
  private static instance: Singleton | null

  public static getInstance(): Singleton {
    if (Singleton.instance)
      return Singleton.instance
    Singleton.instance = new Singleton()
    return Singleton.instance
  }

  private constructor() {
  }
}

Functionバージョン

function genGetInstanceMethod() {
  let instance;

  class Singleton {

  }
  
  // getInstanceをmethodとして返す
  return () => {
    // Closureを利用する
    if (instance == null) {
      instance = new Singleton()
    }
    return instance
  }
}

const getInstance = genGetInstanceMethod()
const i1 = getInstance()
const i2 = getInstance()

console.log(i1 === i2) // true
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