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/**
* This file is part of Haketilo.
*
* Function: Wrap APIs that depend on some asynchronous initialization into
* promises.
*
* Copyright (C) 2021 Wojtek Kosior
* Redistribution terms are gathered in the `copyright' file.
*/
/*
* 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);
}
/*
* EXPORTS_START
* EXPORT make_once
* EXPORTS_END
*/
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