Reject a Promise in JavaScript

Reject a Promise in JavaScript – onlinecode

Reject a Promise in JavaScript

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The Promise.reject() function is the most concise way to
create a rejected promise that contains a given error. You
should then use .catch() to handle the error.

const p = Promise.reject(new Error('Oops!'));

return p.catch(err => {
  err.message; // 'Oops!'

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);

To reject a promise from the executor function, you should just call
reject() with an error object.

const p = new Promise((resolve, reject) => {
  reject(new Error('Oops!'));

return p.catch(err => {
  err.message; // 'Oops!'

Reject With Non-Error

You can reject a promise with any value, not just an error object.

const p = Promise.reject(42);

return p.catch(err => {
  err; // 42

However, many libraries and frameworks assume that promises are always
rejected with an error. So you should be careful if you choose to
call Promise.reject() with a value that isn’t an error.

JavaScript Fundamentals to Reject a Promise in JavaScript

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 for Reject a Promise in JavaScript!

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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