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Використання обіцянок JavaScript для ефективних асинхронних операцій

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Використання обіцянок JavaScript для ефективних асинхронних операцій image

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What are JavaScript promises used for?

JavaScript promises are used for handling asynchronous operations more efficiently by providing a way to deal with operations that haven’t completed yet. They help in organizing and chaining multiple asynchronous tasks.

How do promises work in JavaScript?

Promises are objects representing the eventual completion or failure of an asynchronous operation. They have three states: pending, fulfilled, or rejected. You can attach callbacks to handle the success or failure of the operation.

How do you create a new promise in JavaScript?

To create a promise, you use the Promise constructor with two arguments: resolve and reject, which are functions. Inside the promise, you perform your asynchronous operations and call either resolve or reject based on the outcome.

How can you handle the result of a promise in JavaScript?

You can handle the result of a promise using the `.then()` and `.catch()` methods. The `.then()` method is used to handle the successful completion of a promise, while the `.catch()` method is used to handle any errors or rejections.

How do you chain promises in JavaScript?

You can chain promises using the `.then()` method. Each `.then()` call returns a new promise, allowing you to chain multiple asynchronous operations in a sequence. This helps in avoiding the callback hell and keeps your code clean and organized.

What is a promise.all() method in JavaScript?

The `Promise.all()` method takes an array of promises as an input and returns a single promise that resolves when all of the input promises have resolved. It is useful when you need to wait for multiple asynchronous tasks to complete before proceeding.

How do you use async/await with promises in JavaScript?

The `async/await` syntax provides a more concise way to work with promises. You mark a function as `async`, which allows you to use the `await` keyword inside the function to wait for a promise to resolve before proceeding with further code execution.

Can promises be consumed multiple times in JavaScript?

No, once a promise is resolved or rejected, its result is set and cannot be changed. However, you can create new promises based on the original promise to reuse it in different parts of your code.

How do you handle errors in promises in JavaScript?

You can handle errors in promises by using the `.catch()` method to catch any rejected promises and perform error handling. Additionally, you can use try/catch blocks with async/await to handle errors in a synchronous style.

What are the benefits of using promises in JavaScript?

Promises help in writing cleaner and more readable asynchronous code by providing a standardized way to deal with asynchronous operations. They also make error handling easier and allow for better control flow management in your application.
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