var CreateDiv = function(html) {
	this.html = html;
	this.init();
};
CreateDiv.prototype.init = function() {
	var div = document.createElement('div');
	div.innerHTML = this.html;
	document.body.appendChild(div);
}
var ProxySingletonCreateDiv = (function() {
	var instance;
	return function(html) {
		if (!instance) {
			instance = new CreateDiv(html);
		}
		return instance;
	}
})();
var a = new ProxySingletonCreateDiv('seven1');
var b = new ProxySingletonCreateDiv('seven2');
console.log(a === b); // true

// 通用的单例验证方法
const getSingle = function (fn){
	let result;
	return function (){
		return result || (result = fn.apply(this, arguments));
	};
};
// 创建登录模态框
const createLoginLayer = function (){
	const div = document.createElement('div');
	div.innerHTML = '我是登录模态框';
	document.body.appendChild(div);
	return div;
};
// 为登录模态框使用单例模式
const createSingleLoginLoyer = getSingle(createLoginLayer);
const loginLayer1 = createSingleLoginLoyer(); // 第一个登录模态框
const loginLayer2 = createSingleLoginLoyer(); // 还是第一个登录模态框
console.log(loginLayer1 === loginLayer2); // true

const createLoginLayer = (function (){
	let div;
	return function (){
		if (!div) {
			div = document.createElement('div');
			div.innerHTML = '我是登录模态框';
		}
		return div;
	};
})();

// 在点击按钮时才创建节点（惰性）
document.getElementById('login-btn').onclick = function (){
	var loginLayer = createLoginLayer();
	loginLayer.style.display = 'block';
};