[JavaScript] 单例模式

特点	一个类只能构造出唯一实例
条件	1.确保只有一个实例 ; 2.可以全局访问
适用	适用于弹框的实现, 全局缓存

实现单例模式

const singleton = function(name) {
  this.name = name
  this.instance = null
}

singleton.prototype.getName = function() {
  console.log(this.name)
}

singleton.getInstance = function(name) {
  if (!this.instance) { // 关键语句
    this.instance = new singleton(name)
  }
  return this.instance
}

// test
const a = singleton.getInstance('a') // 通过 getInstance 来获取实例
const b = singleton.getInstance('b')
console.log(a === b)

弹框层的实践

const createLoginLayer = function() {
  const div = document.createElement('div');
  div.innerHTML = '登入浮框';
  div.style.display = 'none';
  document.body.appendChild(div);
  return div;
}

const getSingle = function(fn) {
  let result;
  return function() {
    return result || (result = fn.apply(this, arguments));
  }
}

const createSingleLoginLayer = getSingle(createLoginLayer);

document.getElementById('loginBtn').onclick = function() {
  let loginLayer = createSingleLoginLayer();
  if( createSingleLoginLayer().style.display == "none" ){
    loginLayer.style.display = 'block';
  }else{
    loginLayer.style.display = 'none';
  }
  
}