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  • all right.

  • It's time.

  • Yes, eight.

  • I have never talked about Yes, eight before.

  • But this video, I'm going to look at something called a sink and a weight.

  • And it's part of S eight, which is, yes, 2017.

  • But anyway, this is really what's often referred to as syntax sugar.

  • So basically, we're not going to get any new functionality.

  • But we're going to have a different way to write in a synchronous function that returns a promise that just makes things easier to follow and nicer, I think.

  • I mean, you can choose to decide whether it's better or not, but I think I like it.

  • It's new for me.

  • I haven't really worked with this until yesterday, so let's see how this goes.

  • All right, So just to review, if you watch the previous video I wrote this function called Delay.

  • This function, called DeLay, returns anew.

  • Promise and up.

  • There's one mistake here, so this isn't that big of a deal.

  • Once the promises rejected, I really should stop but not do anything else.

  • But this code keeps going and calls this set time out.

  • It won't resolve the promise, but still doing this weird set time out, so I could There's some options here.

  • I could say, like, return.

  • Um, I could also I think what I'm just gonna do for my way I like to do things is just putting else here.

  • So I'm gonna add that to dysfunction.

  • Receives a number, creates a promise.

  • Oh, receives an argument if the receives a perimeter, if the parameter is not a number, it rejects the promise and throws it an error.

  • If it is, it calls set time out and resolve the promise.

  • That way I can say after a certain delay, like 1000 milliseconds create a paragraph or catch the air.

  • So now what I'm gonna do is I'm going to write DeLay s eight.

  • So here's the thing.

  • If a function returns a promise, if a function returns a promise and what returns a promise, the delay function returns a promise.

  • So I'm gonna do something weird here.

  • Um, so I'm gonna What I want to do is call DeLay e s eight.

  • I'm just I'm writing a new function.

  • I'm gonna call that this is going to stay exactly the same.

  • This is going to stay exactly the same Now, this is really weird.

  • And you know what?

  • The next video.

  • I'm gonna do this with the word Nick and Giffey example that's gonna make way more sense.

  • I probably just do that now, but I'm already going down there.

  • You can skip to the next video if you want.

  • This is a little bit weird.

  • You almost want to forget Pretend that delay isn't a function that I wrote.

  • But DeLay is a function that's part of some JavaScript library that I've imported and DeLay returns A promise.

  • So I'm trying to have a better name for this than DeLay s eight, but I guess I'll keep that right now.

  • Um, so what this allows me to do, right?

  • If a function this function, I've been taking a long time to get to this returns A promise.

  • If that's the case, I can suddenly use this key word await meaning.

  • Just wait for the promise to resolve.

  • It's almost like it's kind of like writing blocking code so I could say await delay time, await delay time.

  • Then I can return.

  • Now.

  • This is why I really want to do this with the fetch function, because there's so much more.

  • This is like a very tiny little bit.

  • But this now should it's gonna make much more sense when I actually have to do more steps, Do anything, just awaiting that.

  • I don't do anything after, but this now will automatically return problems.

  • I'm missing an important piece.

  • Let's just run this and see what happens.

  • I don't know if I like this video so far.

  • It might have toe rethink this, but I'm going.

  • I'm going.

  • I'm going with it.

  • Let me refresh.

  • Await is on Lee Valid in an AI think function.

  • Oh dear.

  • So here's the thing.

  • The await keyword kid, Just use it anywhere in your code like Oh, wait for this.

  • Then do this then wait for this.

  • You have to write your own a synchronous function.

  • Basically, you have to write a function that returns a promise.

  • But rather than having to say new return return new promise.

  • The A sink keyword just says, Hey, do all that stuff kind of invisibly behind the scenes for me.

  • So now if I come back over here and I tag this function, basically attacking is the wrong word, but I modify by giving this function of modifier a sink.

  • I say this is an a synchronous function.

  • It's going to execute a synchronously and and when and return a promise.

  • After all, after however many calls to await that I want.

  • So now let me just hit refresh here and this works again.

  • So this now is an asynchronous function.

  • So this and the reason why this is exciting is I can start to do this so I can sequence a bunch of things that are a synchronous that and and and some of these might actually return something.

  • And this now, instead of having to chain all these different promises with then dot Tenn dot then that then that Then catch this catch that I could just do it all in one function and that function will return a promise.

  • So I think I don't know how much I don't know if this was that useful to you, hopefully gives you kind of a sense, but I think a practical example will make a lot more sense.

  • So if you remember this particular example, look at what I had to do here I had to fetch from word Nick.

  • Then get the response converted to Jason.

  • Then convert that.

  • Then get the word out of that, then go to another A p I I'm going to rewrite all of this in an asynchronous function using a wait.

  • And I think that's going to help make things make more sense.

  • So that's what's gonna be in the next video.

  • Okay, See you there.

  • Maybe, maybe not.

all right.

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16.13: async/await 第1部分--JavaScript/ES8主題 (16.13: async/await Part 1 - Topics of JavaScript/ES8)

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    林宜悉 發佈於 2021 年 01 月 14 日
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