Haketilo

/**

 * Myext feature initialization promise

 *

 * Copyright (C) 2021 Wojtek Kosior

 * Redistribution terms are gathered in the `copyright' file.

 */

"use strict";

/*

 * This module provides an easy way to wrap an async function into a promise

 * so that it only gets executed once.

 */

(() => {

    async function assign_result(state, result_producer)

    {

	state.result = await result_producer();

	state.ready = true;

	for (let cb of state.waiting)

	    setTimeout(cb, 0, state.result);

	state.waiting = undefined;

    }

    async function get_result(state)

    {

	if (state.ready)

	    return state.result;

	return new Promise((resolve, reject) => state.waiting.push(resolve));

    }

    function make_once(result_producer)

    {

	let state = {waiting : [], ready : false, result : undefined};

	assign_result(state, result_producer);

	return () => get_result(state);

    }

    window.make_once = make_once;

})();