How Do I Access the Resolved Value of a Chained Promise in JavaScript?

Understanding Promise Value Access

promesas are ubiquitous in modern JavaScript, allowing for asynchronous operations. While their use is well documented, certain aspects can be confusing. One common question is how to access the value of a promise, especially when promises are chained through the .then() method.

In the example provided, promiseB is created from promiseA. The documentation states that promiseB will hold a value equal to result 1 after promiseA resolves. However, it's not immediately clear how to access this value.

Accessing Promise Values

The key to understanding this is that the .then() method returns a new promise that resolves after the original promise (in this case, promiseA) resolves. The value of this new promise is determined by whatever is returned from the success callback function.

In the provided example, the success callback returns result 1, which means that promiseB will resolve with this value. To access this value, you would use promiseB.then(function(result) {...}) in the same way you would access promiseA.

Async/Await Syntax

ECMAScript 2016 (ES7) introduced async/await syntax, which provides an alternative to the .then() method for working with promises. Using async/await, you can directly access the value of a promise by using the await keyword.

For example, instead of writing:

promiseB.then(function(result) {
    // Use the result
});

You can write:

async function doSomething() {
    const result = await promiseB;
    // Use the result
}

However, note that async/await can only be used within an async function.

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