JavaScript Promises Crash Course

⌚ Timestamps
00:00 - Introduction
01:40 - Creating a promise
03:50 - Errors and catch
05:20 - Chaining multiple methods
07:42 - Using finally
08:54 - Practical examples
14:05 - async and await
16:45 - gotchas with async and await
22:00 - Which approach should you use?

#css

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[teugene]

I wish Chris has a YouTube channel with lessons like this. The way he explains JS is so easy to absorb and understand.

[BMikel]

Please please more JavaScript tutorials. This is good stuff always in demand.

[LordValtrius]

One thing that was skirted around but not touched on is that a promise saved to a variable but isn't chained will cache it's value for future then's, making it perfect for caching since most caches only check if the value exists and sends another request, not if the value is being fetched. Eg:

const question = Promise.resolve(42)

question.then(answer => console.log(answer))
question.then(answer => console.log(answer))

You get 42 logged twice, but if you were to chain them instead, the second would log undefined since nothing is returned from the first.

Great video too, keep it up.

[raystorer]

Kevin, thanks for having Christopher on to explain Javascript promises. He did a great job!

[tazerah]

Chris is a great teacher, but I'd love to see you engage more in the topic when you have guests on! Maybe re-contextualize the subject in a way that was helpful for you, or ask questions that you think a beginner might ask.

Love the videos, Kevin. Thanks!

[markayyy]

This was a great explanation and definitely furthered my understanding. Please make more JavaScript videos like this, they help so much. Many thanks!

[bryanmyers]

I'm really loving these JavaScript videos. The timing is perfect for me because I'm refreshing my skills before going out for a job. Chris is one of the best teachers I've ever seen for this. Very organized and clearly communicated.

[daveturnbull]

Saw the title of this and instantly started preparing my braincell to be blown away. This is a topic I've struggled with from the moment they were introduced.

[flpflpflp]

Really good video, thank you both for taking the time to record it!

[osamudiameh_sama]

I pumped my fist when I saw the notification, promises been giving me a tough time. Thanks for this kev

[mathiascunault]

clear and precise with increasing complexitiy. More stuff like this ! 🙏

[whatisthis__]

I don't know why people keep saying in tutorials that applying the .json() method to a response (for example) gives you a JSON object, when actually it returns a JS object (plain old regular object). That must confuse a lot of people

[hoshi]

I love that you are doing these javascript dives but if I wanted a dictionary definition of these things, I can just read a dictionary. This didn't answer the questions that I needed answered for me to actually understand promises. I needed him to explain what people did before promises existed. How did they get stuff done without a promise style function and how did promises then improve their life using examples. I also needed to get more real world situations where a developer comes across an issue and thinks, "this is exactly where I should use a promise." I write javascript web apps myself and I have never used a promise. Should I be using them? Why, if I am already living life without them? How can they help me. He needed to show code solutions without promises and then show the problematic nature of that and then bring along the hero "dun dda da dan !!! The Promise!" and show how that brings light to the problem. All he does in these videos is read from a dictionary of what a promise is. that is not helpful. Please make the video again but do it in the format that I have suggested here.

[jonux]

Thanks kevin and Chris, finally understand promises and async await functions, greetings from Argentina!!

[aditideshpande]

i genuinely admire you guys for all the knowledge you give us! thanks so much Kevin and Chris! 🎉

[jfftck]

If you ever hear someone talking about a function’s color, it is just saying that asynchronous and synchronous functions are a different “color” and you can only use synchronous functions inside asynchronous ones, but not the other way around. It is just easier to remember that async doesn’t return a value directly, so to wait for it, but to be able to do anything else, you will also need to wait for the parent function as well, all the way until the top function is reached. This is one of the most common issues new developers encounter and have difficulty with understanding.

This video didn’t explain how asynchronous functions work inside the JavaScript runtime, but the simple explanation is that there are three ways functions return a value: just calling a regular, callback for an event, or resolving a promise. So, there is a loop that checks stacks for code to run and it has to check three of them, the first stack is ran immediately, and the next two are added to the first when the condition has been met — like the event being triggered or the promise resolved/rejected. That is why you can’t call asynchronous functions inside synchronous ones, they don’t exist yet in the stack and will only exist after the next iteration of the loop.

[bobmonsour]

Today I learned about "finally." Finally! Personally, I prefer the async/await approach as that is how I first began to understand Promises.

[JohnSmith-opls]

Async, Await. It’s not the dark ages.

[ittixen]

I love those. I was hoping he'd mention how promises returned from another promise kinda automagically get then()'ed, because it really tripped me up when I was first learning promises, and honestly I still to this day didn't manage to wrap my head around it.

[modi_hemnt]

Loved this tutorial!! Please more of this.