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

Tips for inputting information without redundancy after selecting a specific designation

What is the best way to eliminate "?" from the URL while transferring data through the link component in next.js?

Struggling to find the definition of a Typescript decorator after importing it from a separate file

Create a POST request to the server using Express.js

Button click not functioning to switch the displayed image in Javascript

Helping React and MUI components become mobile responsive - Seeking guidance to make it happen

Is it necessary to use callbacks when using mongoose's findbyid with express to retrieve an object from the database? Are callbacks still important in modern JavaScript frameworks?

What is the best way to set up TypeScript to utilize multiple node_modules directories in conjunction with the Webpack DLL plugin?

Difficulty adding extra arguments to a function

When the request's credentials mode is set to 'include', the 'Access-Control-Allow-Origin' header in the response should not be using the wildcard '*'

What is the best way to conceal an element in jQuery by utilizing a JavaScript variable?

Is it possible to modify parameter values while transitioning?

Taking steps when a number is enclosed within a span

How to deal with jQuery's set val() behavior on SELECT when there is no matching value

The use of jQuery.parseJSON is ineffective for a specific string

Tips for displaying a combobox popover from @reach/combobox within a MUI dialog element

Receiving CORS response from the server for just one of the two API calls

Unable to obtain return value in AngularJS controller or view

Having trouble adjusting the label fontSize in ReactJS when using semantic-ui-react?

Tips on running jQuery scripts when a div changes its display style from none to block?