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Welcome back.

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Today, we're going to learn about E.S. 11 or is 20, 20, so this ECMAScript was released in 2020.

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So congratulations, ladies and gentlemen, you are very, very successful.

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So we started from the scratch and now we are here.

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But today we're not going to jump straight to iOS 11 features.

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So I'm going to go back to Essex and I'm going to mention four methods for promises that we haven't

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covered.

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And we haven't covered this for a reason, because in the year 2020, there is a new method released

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for these promises.

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And I knew then and I knew it now that if I just include it in one place instead of including 50 lecture's

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before, then you will pretty much forget about it.

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And we don't we didn't use them until now, maybe.

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Actually, I've used it only once in, but that was not something very important.

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So I haven't used these six features, but I'm going to use it now.

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I'm going to use them now.

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And I need to show you all of this because I will not be able to explain all of the year 2020 features.

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So you haven't missed out anything before.

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Right now it's the time to start working on them.

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So let's start.

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So is six.

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So these are your six promises.

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So before you six implementation, we have a promise is implemented in a libraries like Bluebird or

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Q Right.

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Thank now now S6 or is 2015 promises are implemented as a standard standard part of JavaScript core

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language.

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So we have old method race method to reject and result in.

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These are implemented in promises class.

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So this is promise class nice so we can make more instances of now promise.

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The old method takes in the iterable all the promises as an input.

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So that can be a real overpromises.

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Right.

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And returns back a single promise that resolves to an array of results.

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What.

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OK, so let's start coding.

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So first things first.

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I'm going to create const promise one equal new promise here so we make sense of this class here.

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Are we going to see whether it will be resolved or rejected?

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So I'm going to say resolve or reject here and I'm going to pass the error function in inside here.

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We're going to mention the set timeout function right now.

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This set time, our function is super important for us.

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Why?

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Because we haven't used it until now cuz now the set out function we haven't used actually in years

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since before we used it, when I was explaining the promise in this set time, I will never feel right.

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It will always execute.

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It's not like an API that can go wrong.

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That's why here we are going to pass the resolve in the milliseconds when they should kick in.

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And this is the value that I want to restore.

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Promise one.

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Let's compare this promise based at two times and change this to two as well here, too,

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and the last one to three and change it back to three.

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Now, what's the Syntex?

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Let's be sure that you put a semicolon there.

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You don't have to.

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That what's the syntax.

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So promise that all in here is.

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I told you it takes an iterable.

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Overpromises or an array is an input in here.

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I'm going to jam all of this.

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Promise one.

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Promise to and promise three.

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Right.

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Good.

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And what I can do here, I'm going to attach the then method.

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And I'm going to simply data and control this data so we can move this one a little bit down here and

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I'm going to console lock the data, that is pretty much what I can do here.

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Actually, let's not finish it here.

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Attach that catch.

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And in this catch here, I'm going to parse the error like that.

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And simply, I'm going to counsel and I'm going to see error occurred in one of the promises above.

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Space here, exclamation mark, and as well, I'm going to just print out the air nice.

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So these all three promises are resolved.

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So here is the syntax.

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Is this Brahmas that all Jammal, the promise is here as an input or as an array?

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And here I'm not doing anything special on this, bringing out the data or if it's any error I'm going

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to catch.

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But I know it will not be error because this is a satima function.

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It will always resolve the truth.

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Right.

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If we don't specify reject here, it will always be true.

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But here we need to change one thing.

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It's a five hundred milliseconds for the first one.

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Make thousand loops.

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Make thousand for and a second.

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Second one and let's make two thousand for the third one.

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These are all in milliseconds.

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OK, copied interring.

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Go to Google Chrome.

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I suggest you to use the Google Chrome based in here and enter now the promise will be pending and now

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all of the promises are resolved in the output, as I told you, is an array of resolved promises.

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So we have promised one promise to promise three.

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Cool.

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But what what will happen if I reject one of them here?

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You know, OK, save it, refresh F5 or hit here, spending Arakwal in one of the promise and I'm catching

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that everything I promise to where we have that promise rejected, now it reject immediately upon any

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of the input promises we rejected and where or where there is a throne in there and it will reject with

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the first rejection message or the error that we just got.

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So the problem is that this is something that you shouldn't need.

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You should know if we have any rejection here, it will stop of executing and it will throw it immediately.

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So that is all that you need to know about promise.

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Oh, now I have another one interesting promise race.

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And actually here I'm going to keep it interesting, same as this one.

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We're going to make a couple of changes here, one, two and three right now.

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We also need to change this promise, that race.

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So first, let me write it down and I'm going to explain what will happen here.

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Now, let's go back here and see now.

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Promise one.

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It's equal to the new promise.

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We will resolve them.

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Let's put here a hundred and say promise one.

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The promise you will be five hundred

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in the promise three will be again here is not going to be rejected.

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Actually make sure it's resolved.

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And the promise three will be how much.

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Let's put the promise three or fifty.

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So that is half of the first one and we saying it to resolve.

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You now promise that race here in passing the year.

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But I need to promise one promise

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misto and I have the promise.

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Three, Don't forget to change this because we have a different conference here.

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Right.

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And I have then data Konza lock that data or whatever you want.

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So what do you think is going to be what is going to happen?

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What is the expected output?

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OK.

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Let's refresh let's face this one here, hit enter, promised more spending and promise three.

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Well, why is this is happening?

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Why I don't go from the first, second and third promise three has been resolved, but it's 50 milliseconds

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right now.

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What is a promise that race.

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So this is actually a race between three promises to the race method returns.

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A promise that fulfills or rejects doesn't matter.

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As soon as one of the promises of this iterable here, Arae fulfills or rejects.

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So with the value, actually, with the value of this, with the value of the reason for from that promise.

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Nice.

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So this returns a promise that rejects or Fairfield's as soon as one of the promises here from this

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iterable fulfills or rejects.

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And I'm just pointing out the value.

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OK, what you think will happen if I put it here, reject, would you think that the first one will

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go first?

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Let's see.

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Save it.

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Clearing the east and enter.

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No I haven't got er undefined identifier promise.

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One has already been declared.

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Cool refresh again.

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Pasted down here.

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Nice because I have to refresh and I this new cause that needs to be fresh.

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Right.

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So Kirkorian one of the promises above promised three.

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Very good.

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But this is the first promise that rejected.

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Right.

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So it doesn't matter if it's going to reject or fulfill.

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That is the one the first going to raise.

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So that's that's going to be actually the winner of this race.

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Nice.

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So we have promises o promise.

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We get a raise and we have promised results.

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Now, promise resolve is OK, actually.

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Sorry, promise project.

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We're going to promise project.

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It's a method to return a promise object that is rejected with a given reason.

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Right.

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So the static promise reject function returns a promise that is rejected.

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This is good for debugging or catching an error.

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Selective error.

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So it is useful to make a reasons of an instance of an error.

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Nice.

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So here I'm going to say promis reject in.

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You will see what I try what I did say like a couple of seconds ago.

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So promise we need to call the class reject in here.

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I'm going to throw a new error and the description goes here, feel nice, I'm going to use that method

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and I can pass a function here.

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Right.

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So this function will not take any parameters.

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But what will happen?

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This bar will never be called.

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Right.

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I'm going to add a function, another comma here.

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I'm going to add another function.

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And actually here I'm going to catch the error.

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What's happening?

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Why so cancel the error.

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Actually, we're going to say this is promise.

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Reject it.

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I'm going to see the error note.

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So when we have a then method attached with the reject, that method will never go and be executed.

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It will go straight to the rest of the code right here.

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We are throwing an error.

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So the promised reject method returns a promise that is rejected with the given reason.

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It was the reason you just throwing up an error.

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This is good for debugging purposes or for error, catching more for anything that you want to test

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it out.

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Let's copy it here.

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Based it down there.

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Hit enter.

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Here it is.

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This is the promised reject error and field comes from the value past into this error.

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Nice.

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So every time we use reject, we know that the method will return a promise object that is rejected

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for a given reason.

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I'm going to copy the same thing same and I'm going to based it down here.

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It's going to say promise is resolved.

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Now this is the opposite.

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We need to use the syntax promise that resolve cool in here instead of error.

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You can print out our success message.

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Now we have the then function where it will take a value here and we will cancel the value.

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What you think we'll print here, the function error.

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Actually, this will never execute.

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Because this is totally opposite than this one, when we have a dinner, everything that is there is

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going to be executed.

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Now the problem is resolved.

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Again, going to return a promise object, but it's going to be resolved with the given value.

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And the value is here.

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We passing here in capacity.

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They can pass value, whatever it is.

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Now, if there is a dead method, it will go there.

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Right.

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OK, no, copy it here.

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Based on our success, again, the promised state is fulfilled and the results of the undefined right

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now, it will never go to this one.

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This is a promise project error.

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Actually, we don't need to see a promised project because we never said we're going to go there now.

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That's it.

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So, you know about all the promises.

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So we have a class for the promises and we can use one, two, three, four methods.

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Right.

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So this actually takes as an argument here on the array of promises.

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And as soon as they're fulfilled or rejected, it will go through here.

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So if they reject it, it will be stopped.

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We don't we're not going to have as a result at the end, an array of results, promises, promises

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that race.

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So we are just seeing here, OK, we have three promises, regardless of it's rejected or resolved.

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The one with these fasters fastest, it will go there.

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Right.

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And the we do have the promised reject and promised results, which are very simple and easy to understand.

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These will always reject.

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And we need to give the specify the reason it's good for debugging.

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And this will always be successful.

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And we are just going to print it out here then always this method that will go here, it will be executed.

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Right.

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So now if you have something important that you want to be executed, no matter what, she's going to

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put it here.

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That's it.

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So thank you very much.

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Next lecture, we're going to learn a lot more things and we are going to introduce new method into

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2020 that is important and connected with this.

248
00:16:02,790 --> 00:16:05,510
OK, so I will see you in the next one.