Thenables in JavaScript – onlinecode
In this post, we will give you information about Thenables in JavaScript – onlinecode. Here we will give you detail about Thenables in JavaScript – onlinecode And how to use it also give you a demo for it if it is necessary
In JavaScript, a thenable is an object that has a then() function. All promises are thenables, but not
all thenables are promises.
Many promise patterns, like chaining
and async/await, work with any
thenable. For example, you can use thenables in a promise chain:
// A thenable is an object with a 'then()' function. The
// below thenable behaves like a promise that fulfills with
// the value '42' after 10ms.
const thenable = {
then: function(onFulfilled) {
setTimeout(() => onFulfilled(42), 10);
}
};
Promise.resolve().
then(() => thenable).
then(v => {
v; // 42
});You can also use thenables with await:
// A thenable is an object with a 'then()' function. The
// below thenable behaves like a promise that fulfills with
// the value '42' after 10ms.
const thenable = {
then: function(onFulfilled) {
setTimeout(() => onFulfilled(42), 10);
}
};
const v = await thenable;
v; // 42Thenables in the Wild
Many libraries implement thenables to enable async/await support.
For example, Mongoose queries are
thenables, although they also have an exec() function that returns
a promise. Superagent is
a popular HTTP client that also uses thenables. However, neither
Mongoose queries nor Superagent requests are actually promises.
Other libraries use promises directly. For example, Axios requests are promises in the sense that they are instanceof Promise.
You can convert an arbitrary thenable to a promise using Promise.resolve():
// A thenable is an object with a 'then()' function. The
// below thenable behaves like a promise that fulfills with
// the value '42' after 10ms.
const thenable = {
then: function(onFulfilled) {
setTimeout(() => onFulfilled(42), 10);
}
};
const p = Promise.resolve(thenable);
p instanceof Promise; // true
const v = await p;
v; // 42
JavaScript Fundamen for Thenables 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
varkeyword. - 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.
- JavaScript.info: JavaScript.info 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 Thenables 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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