The catch method is used to handle a promise when it's rejected. It also takes a callback function as a parameter. The callback function takes the rejected value as a parameter.
Let's take the same example of the rocketLaunch promise from the previous lesson and see how to use the catch method to handle the promise when it's rejected. We'll set the value of the launchSuccess variable to false to simulate a rejected promise.
If we run the above code, the output will be:
Here the reject method is called instead of the resolve method because the launchSuccess variable is set to false. A promise is rejected when the reject method is called. Since the promise is rejected, the catch method is called, and the rejected value is passed to the callback function. In this case, the rejected value is Uh-oh, the rocket launch encountered a problem..
If you notice the above code, you'll see that we're repeating the same code console.log("Rocket launch process completed."); in both the then and catch methods. We can avoid this repetition by using the finally method.
We'll learn about the finally method in the next lesson.