定义
只有一个实例，并提供全局访问。
实现
思路：用一个变量来标识当前是否已经为某个类创建过对象，如果是，则在下一次获取该类的实例时，直接返回之前创建的对象，否则返回新对象。
饿汉模式
特点：类加载时就初始化。
class Singleton {
private static instance = new Singleton()
// 将 constructor 设为私有属性，防止 new 调用
private constructor () {}
static getInstance (): Singleton {
return Singleton.instance
}
}
const singleton1 = Singleton.getInstance()
const singleton2 = Singleton.getInstance()
console.log(singleton1 === singleton2) // true
懒汉模式
特点：需要时才创建对象实例。
class Singleton {
private static instance: Singleton
private constructor () {}
static getInstance (): Singleton {
if (!Singleton.instance) {
Singleton.instance = new Singleton()
}
return this.instance
}
}
const singleton1 = Singleton.getInstance()
const singleton2 = Singleton.getInstance()
console.log(singleton1 === singleton2) // true
简单栗子
class Singleton {
private constructor (name: string, age: number) {
this.name = name
this.age = age
}
private static instance: Singleton
public name: string
public age: number
static getInstance (
name: string,
age: number
): Singleton {
if (!this.instance) {
this.instance = new Singleton(name, age)
}
return this.instance
}
}
const singleton1 = Singleton.getInstance('Mary', 20)
const singleton2 = Singleton.getInstance('Jack', 20)
console.log(singleton1, singleton2)
