compose-async

compose-async.js

function isAsync(fn) {
    return fn.constructor.name === 'AsyncFunction';
}

const compose = (...fns) => {
    let containsAsync = false;
    return function (param) {
        let result = param;
        while (fns.length) {
            let currentFn = fns.shift();
            if (containsAsync) {
                result = result.then(currentFn);
            } else {
                if (isAsync(currentFn)) {
                    containsAsync = true;
                    result = Promise.resolve(currentFn(result));
                } else {
                    result = currentFn(result);
                }
            }
        }
        return result;
    }
}

const func1 = string => string.toUpperCase();

const func2 = async param => {
    return param.substring(1, 3);
};

const func3 = string => {
    const first = string[0];
    return [first, first, first].join("");
};

const exe = compose(func1, func2, func3);

(async () => {
    try {
        const result = await exe("hello");
        console.log(result);
    } catch (error) {
        console.log(error);
    }
})();