source: imaps-frontend/node_modules/is-async-function/index.js

'use strict';

var toStr = Object.prototype.toString;
var fnToStr = Function.prototype.toString;
var isFnRegex = /^\s*async(?:\s+function(?:\s+|\()|\s*\()/;
var hasToStringTag = require('has-tostringtag/shams')();
var getProto = Object.getPrototypeOf;
var getAsyncFunc = function () { // eslint-disable-line consistent-return
        if (!hasToStringTag) {
                return false;
        }
        try {
                return Function('return async function () {}')();
        } catch (e) {
        }
};
var AsyncFunction;

module.exports = function isAsyncFunction(fn) {
        if (typeof fn !== 'function') {
                return false;
        }
        if (isFnRegex.test(fnToStr.call(fn))) {
                return true;
        }
        if (!hasToStringTag) {
                var str = toStr.call(fn);
                return str === '[object AsyncFunction]';
        }
        if (!getProto) {
                return false;
        }
        if (typeof AsyncFunction === 'undefined') {
                var asyncFunc = getAsyncFunc();
                AsyncFunction = asyncFunc ? getProto(asyncFunc) : false;
        }
        return getProto(fn) === AsyncFunction;
};