index.js

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
    typeof define === 'function' && define.amd ? define(factory) :
    (global.module = factory());
}(this, (function () { 'use strict';

function once(fn) {
    if (!(fn instanceof Promise || typeof fn === 'function')) {
        throw new Error('arguments "fn" must be async function');
    }

    var queue = [];
    var running = false;
    var result = null;

    var runQueue = function runQueue() {
        running = false;
        queue.forEach(function (_ref) {
            var resolve = _ref.resolve,
                reject = _ref.reject;

            result ? resolve(result) : reject();
        });
        queue.length = 0;
    };

    return function () {
        for (var _len = arguments.length, props = Array(_len), _key = 0; _key < _len; _key++) {
            props[_key] = arguments[_key];
        }

        return new Promise(function (resolve, reject) {
            if (result !== null) {
                resolve(result);
                return;
            }

            if (running) {
                queue.push({ resolve: resolve, reject: reject });
                return;
            }

            running = true;
            (Promise.prototype.isPrototypeOf(fn) ? fn : fn.apply(undefined, props)).then(function (data) {
                result = data;
                runQueue();
                resolve(result);
            }).catch(function (e) {
                runQueue();
                reject(e);
            });
        });
    };
}

// Map
var fnMap = {};
once.onceMap = function (fName, fn) {
    if (fName in fnMap) {
        return fnMap[fName];
    }

    var newFn = once(fn);
    fnMap[fName] = newFn;
    return newFn;
};

return once;

})));
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