Asynchronous programming is a programming paradigm that allows for non-blocking execution of code by running tasks in the background and notifying the program when they are complete.
This is useful for tasks that can take a long time to complete, such as accessing data from a database or fetching data from an external API.
A practical example of asynchronous programming is cooking a meal. When you are cooking a meal, you can start one task (such as chopping vegetables) and then move on to another task (such as boiling water) while the first task is still running. You don't have to wait for the first task to finish before starting the second task.
Similarly, in asynchronous programming, you can start a task and move on to another task without waiting for the first task to complete.
In this example, the
fetchData function takes a URL as an argument and returns a Promise. The Promise represents the eventual completion (or failure) of the task of fetching data from the URL.
The function uses the
XMLHttpRequest object to make a network request to the URL and listens for the
errorevents. If the request is successful, the Promise is resolved with the response data. If the request fails, the Promise is rejected with an error.
In the main program, we call the
fetchData function with a URL and
thenattach a then callback to handle the successful completion of the Promise (which in this case simply logs the response data to the console) and a
catchcallback to handle any errors that may occur during the task.
This allows the program to continue running other tasks while the network request is running in the background, and then handle the result of the request when it is completed.
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