How do I return the response from an Asynchronous Call in Javascript?
JS is a popular interpreted language, used widely in web development. It supports many asynchronous techniques, such as callbacks and promises. Asynchronous calls are a way to run multiple tasks in parallel, without blocking the main thread.
This article will explain how to use callbacks and promises to return the response from an asynchronous call, in JavaScript.
Callbacks
Callbacks are the most basic and commonly used way to handle async calls in JS. A callback is a function that is passed as an argument to another function, which is then called when the asynchronous call is completed.
To return the response from an asynchronous call as a callback, the following steps should be taken:
- Declare a function to handle the response from the asynchronous call, and pass it as a callback argument.
- Make the asynchronous call, passing the callback as an argument.
- Inside the callback function, return the response.
- Use the returned response according to business logic.
Promises
A promise is an object that may produce a single value, which can either be resolved or rejected. A promise allows you to create a chain of asynchronous operations, and handle each response as it comes.
To return the response from an asynchronous call as a promise, the following should be done:
- Make the asynchronous call, and assign it to a promise object
- Provide a resolve() and reject() callback in the promise chain, to handle both the successful and failed states
- Inside the resolve() callback, return the response.
- Use the returned response according to business logic.
In conclusion, JS offers many strategies to efficiently handle async calls. Callbacks and promises are two commonly used approaches, however promises are preferred when handling multiple asynchronous operations. This article explained how to use callbacks and promises to properly return the response from an asynchronous call.
