SOURCE

// 单例模式登录框,全局只有一个弹窗对象
var getSingle = function (fn){
    let resulet
    return function (){
        return resulet || (resulet = fn.apply(this,arguments))
    }
}
let creartShow = function(){
    let div = document.createElement('div')
    div.innerHTML = '全局唯一div'
    div.style.display = 'none' 
    document.body.appendChild(div)
    return div
}
let creartSingShowLog= getSingle(creartShow)

document.getElementById('button_1').onclick = function(){
    let layer = creartSingShowLog()
    layer.style.display = 'block'
}

document.getElementById('button_2').onclick = function(){
    let layer = creartSingShowLog()
    layer.style.display = 'block'
}

// es6 单例模式
class Layer{
 constructor(name,age){
     this.name = name
     this.age = age
 }
 static getInstance(name,age){
     if(!this.instance){
         this.instance = new Layer(name,age)
     }
     return this.instance
 }
}

let a = Layer.getInstance('Kevin',29)
let b = Layer.getInstance('Tom',38)
console.log(a)
console.log(b)
console.log(a===b)

<button id="button_1"> 按钮A</button>
<button id="button_2"> 按钮B</button>