getSingle

getSingle.js

/**
 * [惰性单例]
 * @param  {Function} fn [需要使用单例模式的函数]
 * @return {Function}
 */
function getSingle(fn) {
	var ret
	return (...args) => ret || (ret = fn.apply(this, args))
}

/**
 * Usage
 *
 * var createLoginLayer = function() {
		var div = document.createElement('div')
		div.innerHTML = 'loginLayer'
		div.style.display = 'none'
		document.body.appendChild(div)
		return div
	}

	var createSingleLoginLayer = getSingle(createLoginLayer)

	loginLayer只会被创建一次
 */