Resolve a Promise in JavaScript - onlinecode

Resolve a Promise in JavaScript

Resolve a Promise in JavaScript

In this post, we will give you information about Resolve a Promise in JavaScript. Here we will give you detail about Resolve a Promise in JavaScript And how to use it also give you a demo for it if it is necessary.

The Promise.resolve() function is the most concise way to create a fulfilled promise that contains the given value. For example,
suppose you wanted to create a promise that is fulfilled with the string ‘Hello, World’:

const p = Promise.resolve('Hello, World');

const str = await p;
str; // 'Hello, World'

return p.then(str => {
  str; // 'Hello, World'

Resolved is Not the Same as Fulfilled

Explaining the difference between a promise that is resolved and
a promise that is fulfilled is a common JavaScript interview question.
The difference is subtle, but important.

The key difference is what happens when a promise is resolved with
another promise. When you call Promise.resolve(p), where p is a
promise, you create a new promise that is tied to p. If p is
fulfilled, the returned promise is fulfilled with the same value.
If p is rejected, the returned promise is rejected with the same value.
The Promises/A+ spec calls this process “assimilation”.

const p = Promise.resolve('Hello, World');
const p2 = Promise.resolve(p);

const str = await p2;
// 'p2' "assimilates" the value of 'p'.
str; // 'Hello, World'

A promise that is resolved to another promise is still pending.
In particular, a promise that is resolved can still become rejected!

async function fail() {
  await new Promise(resolve => setTimeout(resolve, 100));
  throw new Error('Oops');

// Calling 'fail()' returns a promise that rejects after
// 100ms. So 'p' will reject, even though it was resolved!
const p = Promise.resolve(fail());

const err = await p.catch(err => err);
err.message; // 'Oops'

Resolved is not a promise state. On the other hand, fulfilled is
one of 3 states a promise can be in, and once a promise transitions
to fulfilled, JavaScript executes any onFulfilled callbacks you passed to the then() function.

With the Promise Constructor

When you create a promise using new, you call the Promise constructor.
The Promise constructor takes a single parameter, an executor function.
The Promise constructor then executes the executor function with 2
arguments: resolve() and reject().

function executor(resolve, reject) {
  typeof resolve; // 'function'
  typeof reject; // 'function'

new Promise(executor);

Note that the first parameter is typically called resolve(), notfulfill.
That’s because the resolve() function in the promise constructor behaves
much like Promise.resolve(). When you call resolve() with a promise,
you “assimilate” the value of that promise.

const p = Promise.resolve('Hello, World');
const p2 = new Promise(resolve => resolve(p));

const str = await p2;
// 'p2' "assimilates" the value of 'p'.
str; // 'Hello, World'

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JavaScript Fundamentals

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

  • Variables: Variables are used to store data. They are declared using the var keyword.
  • Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
  • Operators: Operators are used to perform operations on data.
  • Control flow statements: Control flow statements allow you to control the order in which your code is executed.
  • Functions: Functions are blocks of code that can be reused.
  • Objects: Objects are used to store data in key-value pairs.
  • Arrays: Arrays are used to store data in a sequential order.
  • Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
  • DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

  • Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
  • W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
  • is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps!

Here are some additional tips for learning JavaScript:

  • Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
  • Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
  • Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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