lazy.js

export default lazy

import defer from 'defer'

/**
 * @param {Function} fn
 * @return {Function}
**/
function lazy (fn) {
	return function () {
		var context = this
		var args = arguments

		var real
		var deferred = defer()
		var proxy = deferred.promise
		var resolve = deferred.resolve
		var reject = deferred.reject
		var then = proxy.then

		proxy.then = function (onFulfilled, onRejected) {
			if (!real) {
				real = fn.apply(context, args)
				real.then(resolve, reject)
			}

			return then(onFulfilled, onRejected)
		}

		return proxy
	}
}