Ways to extract repeated value from a function?

Question

Ways to extract repeated value from a function?

Currently, I am working with two files. One file contains a script that generates a token, while the other file handles that token.

The issue arises with the second script, as it only logs the initial token received and does not update with any new values.

This is how I am managing the token:

const first_file = require("./first_file.js");
first_file.first_file().then((res) => {
    console.log(res);
});

Obviously, this approach will not suffice because it does not reflect the updated value of the token.

first_file = async () => {
    return new Promise(async (resolve, reject) => {
        //Generating the token
        (async () => {
            while (true) {
                console.log("Resolving...");
                resolve(token);
                await sleep(5000);
                resolved_token = token;
            }
        })();
    });
};

module.exports = { first_file };

In an attempt to continuously resolve the token, I implemented a while..loop. However, this method proved unsuccessful. Is there a more efficient way to directly export the variable for easier execution?

javascript promise generator

Answer 1

Answer №1

It seems like you are looking to handle promises in JavaScript, but there is a misunderstanding about how promises work.

You cannot resolve a promise multiple times, as it goes against the nature of promises in JavaScript.

Generator Function

However, you can use a generator function to generate new values from a function. This type of function, also known as a generator, allows a function to reenter its context and yield results using the yield keyword, similar to async/await.

Generators are often used in loops like for..of and have a next() method to yield the next value.

For example:

const delay = ms => new Promise(res => setTimeout(res.bind(null, ms), ms));

async function* generator() {
    yield 'yield result from generator!'
    for (let ms = 100; ms <= 300; ms += 100) {
        yield 'delay: ' + await delay(ms) + ' ms';
    }
    yield delay(1000).then(() => 'you can also yield a promise!');
}

async function main() {
    const gen = generator();
    console.log('1st', (await gen.next()).value);
    for await (const ms of gen) {
        console.log(ms)
    }
}

main()

The * after the function indicates that it is a generator. When combined with the async keyword, it becomes an Async Generator.

Generators are versatile and useful for generating values on demand, passing data like a pipe, or returning endless values from a function.

Callback Approach

Another approach is the callback method, commonly used in older Node.js versions, where a callback function is passed as an argument.

Example:

const delay = ms => new Promise(res => setTimeout(res.bind(null, ms), ms));

async function callback(fn) {
    fn('yield result from callback!');
    for (let ms = 100; ms <= 300; ms += 100) {
        fn('delay: ' + await delay(ms) + ' ms');
    }
    await delay(1000);
    fn('yield asynchronously!');
}

callback(value => console.log(value));

Although the callback approach is functional, it can lead to issues such as creating function scope problems, disrupting control flow, and lacking a break keyword. It may not be the most recommended method for handling asynchronous operations.

Answer 2

It seems like you are looking to handle promises in JavaScript, but there is a misunderstanding about how promises work.

You cannot resolve a promise multiple times, as it goes against the nature of promises in JavaScript.

Generator Function

However, you can use a generator function to generate new values from a function. This type of function, also known as a generator, allows a function to reenter its context and yield results using the yield keyword, similar to async/await.

Generators are often used in loops like for..of and have a next() method to yield the next value.

For example:

const delay = ms => new Promise(res => setTimeout(res.bind(null, ms), ms));

async function* generator() {
    yield 'yield result from generator!'
    for (let ms = 100; ms <= 300; ms += 100) {
        yield 'delay: ' + await delay(ms) + ' ms';
    }
    yield delay(1000).then(() => 'you can also yield a promise!');
}

async function main() {
    const gen = generator();
    console.log('1st', (await gen.next()).value);
    for await (const ms of gen) {
        console.log(ms)
    }
}

main()

The * after the function indicates that it is a generator. When combined with the async keyword, it becomes an Async Generator.

Generators are versatile and useful for generating values on demand, passing data like a pipe, or returning endless values from a function.

Callback Approach

Another approach is the callback method, commonly used in older Node.js versions, where a callback function is passed as an argument.

Example:

const delay = ms => new Promise(res => setTimeout(res.bind(null, ms), ms));

async function callback(fn) {
    fn('yield result from callback!');
    for (let ms = 100; ms <= 300; ms += 100) {
        fn('delay: ' + await delay(ms) + ' ms');
    }
    await delay(1000);
    fn('yield asynchronously!');
}

callback(value => console.log(value));

Although the callback approach is functional, it can lead to issues such as creating function scope problems, disrupting control flow, and lacking a break keyword. It may not be the most recommended method for handling asynchronous operations.

Ways to extract repeated value from a function?

Answer №1

Generator Function

Callback Approach

Similar questions

Unable to save and subsequently recover the image

The page remains static even as the function is executed

AngularJS attempting to conceal the popup menu upon clicking outside of the designated area

Unable to generate a fresh directory with mongoose and express

Exploring the process of defining directives with Vue 3's composition API

retrieving data from GET variables and sending to a PHP array

I'm facing an issue with converting my object to an array as I keep getting the message: "ERROR TypeError: undefined

The form is refusing to submit even after using the "return false

Utilizing the power of async/await in combination with the versatile Bluebird library to seamlessly

Customizing Ext JS/Sencha Chart framework based on certain conditions

Looping through an array of data retrieved from the MS Graph API

Sending a form using an AngularJS dropdown menu

I'm running into a "timeout" issue with socket.io and a self-signed SSL connection. Can anyone help me troubleshoot this?

Enhance Your Highcharts Funnel Presentation with Customized Labels

When incorporating Vue as an npm package, a Vue 3 app may inadvertently clear the mounted element upon initialization

Unable to execute functions using an AJAX request

The checkbox must be checked for the conditional form to appear, experiencing a Safari bug in version 12.2. No issues found in Chrome and Firefox browsers

Is it possible for me to include a variable with the xmlhttp response text?

When utilizing a script to deliver a true or false response for jQuery's .load() function

What is the most efficient way to update a specific element in a redux/vuex store?