Reject a Promise and Handle Errors

Now I'll teach you how to handle a rejected Promise. 0:00 If an error occurs, the Promise status changes from pending to a rejected, or 0:03 failed state. 0:08 The good thing is that promises give you the opportunity to handle the error with 0:09 a method called catch. 0:13 I'll start by changing resolve to reject. 0:15 And pass it the string, No! 0:20 There was a problem with your order. 0:23 Now I can call the catch method on breakfastPromise, 0:30 which deals with rejected cases only. 0:33 I can do that by chaining it to the then method, like so. 0:36 The function passed to catch takes one argument, which is the rejection reason, 0:43 or the error message to display. 0:48 I'll pass catch an arrow function that takes the parameter, err, and 0:50 logs it to the console. 0:54 I'll Save my file and run it in the terminal. 0:59 The reject method changes the status of the Promise from pending to rejected. 1:03 So this time, instead of then, catch gets called, 1:08 invoking the function passed to it and in the Console we see the message, No! 1:11 There was a problem with your order. 1:16 Keep in mind that if you don't specify reject and 1:18 a catch method to handle a rejected Promise, the Promise will fail silently. 1:22 Errors will be swallowed up with no side effects to the rest of your app. 1:27 In other words, the program will continue to execute as if everything was fine. 1:32 Now that you know how resolve and reject work, I'm going to write a conditional 1:40 statement inside setTimeout that checks the true and false value of an order. 1:45 Let's have it say if order is true resolve 1:51 this promise to the value Your order is ready. 1:56 Come and get it! 2:03 Else, if it's false, reject the Promise and 2:06 set the rejection reason to Your order cannot be made. 2:11 This time I'm passing the Error object to reject versus only a string. 2:20 While it's not required, it does help with debugging because it will display 2:26 the stack trace alongside the rejection reason. 2:30 All right, so now to test this, 2:32 I'll initialize a variable named order to true. 2:36 I'll run the file in the Console, since order is true, 2:42 the Promise resolves to Your order is ready. 2:45 Come and get it. 2:48 Now, I'll change order to false and run the file again. 2:49 This time the Promise is rejected, so the rejection reason, 2:56 Your order cannot be made, displays in the Console, followed by the stat trace. 3:00 Good, finally to make your code more readable and 3:05 the Promise sequence easier to follow, you can place each then and 3:09 catch call on a separate line like this. 3:14 This approach will come in handy starting in the next step, 3:19 where you'll chain together a sequence of Promises. 3:22