Javascript Promises

A technique to manage asynchronous operations is offered by JavaScript promises. Asynchronous operations are those that don’t prevent the code from running. An HTTP request, an API call, or reading a file from disc are a few examples. Since we can’t always count on the outcome to be available right away, we need a strategy for dealing with it when it is. By allowing for the execution of code when the outcome is ready, promises offer a solution for dealing with such situations.

Syntax:

const promise = new Promise((resolve, reject) => {
  // Perform an asynchronous operation
  // If successful, call resolve(result)
  // If failed, call reject(error)
});

Here, resolve is a function that is called when the operation is successful, and reject is a function that is called when the operation fails. The Promise object returned by the new Promise constructor has two methods: then and catch.

The then method is called when the promise is resolved, and it takes a function that will be executed with the result of the promise as its argument. The catch method is called when the promise is rejected, and it takes a function that will be executed with the error as its argument.

promise.then(result => {
  console.log(result);
}).catch(error => {
  console.error(error);
});

The then and catch methods can be chained together to handle both successful and failed results of the promise.

promise.then(result => {
  console.log(result);
  return anotherPromise();
}).then(anotherResult => {
  console.log(anotherResult);
}).catch(error => {
  console.error(error);
});

A new promise is returned by the second then method in this case, which is only called if the first promise is accepted or denied.

JavaScript promises are a potent tool for managing asynchronous actions, and they make code easier to read and maintain.

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