What are JavaScript PROMISES? 🤞

Рет қаралды 78,757

Күн бұрын

#JavaScript #tutorial #courses
// Promise = An Object that manages asynchronous operations.
// Wrap a Promise Object around {asynchronous code}
// "I promise to return a value"
// DO THESE CHORES IN ORDER
// 1. WALK THE DOG
// 2. CLEAN THE KITCHEN
// 3. TAKE OUT THE TRASH

Пікірлер: 69

@BroCodez 11 ай бұрын

// Promise = An Object that manages asynchronous operations. // Wrap a Promise Object around {asynchronous code} // "I promise to return a value" // PENDING -> RESOLVED or REJECTED // new Promise((resolve, reject) => {asynchronous code}) // DO THESE CHORES IN ORDER // 1. WALK THE DOG // 2. CLEAN THE KITCHEN // 3. TAKE OUT THE TRASH function walkDog(){ return new Promise((resolve, reject) => { setTimeout(() => { const dogWalked = false; if(dogWalked){ resolve("You walk the dog 🐕"); } else{ reject("You DIDN'T walk the dog"); } }, 1500); }); } function cleanKitchen(){ return new Promise((resolve, reject) => { setTimeout(() => { const kitchenCleaned = true; if(kitchenCleaned){ resolve("You clean the kitchen 🧹"); } else{ reject("You DIDN'T clean the kitchen"); } }, 2500); }); } function takeOutTrash(){ return new Promise((resolve, reject) => { setTimeout(() => { const trashTakenOut = true; if(trashTakenOut){ resolve("You take out the trash ♻"); } else{ reject("You DIDN'T take out the trash"); } }, 500); }); } walkDog().then(value => {console.log(value); return cleanKitchen()}) .then(value => {console.log(value); return takeOutTrash()}) .then(value => {console.log(value); console.log("You finished all the chores!")}) .catch(error => console.error(error));

@salimthedon 4 ай бұрын

Thank you bro!You made me understand promises!

@maialso6096 3 ай бұрын

Here some questions that helped me understand the video more ! I'm absolute beginner so don't judge 2:40 1) Why do we need callbacks to do these chores in order? I was wondering why don't we just call the functions like this.. walkDog(); cleanKitchen(); takeOutTrash(); We can't do this because the output is going to be >> You take out the trash >> You walk the dog >> You clean the kitchen So the function that takes less time is going to be executed first. Since we want to make sure that each chore is going to be done after the another in order we have to use callbacks since the next function It will never be called unless the function fully executes 3:10 2) What is Callback hell? is an old pattern to handle asynchronous functions I watched the video Callback hell , and It also answers the first question 3) Why do we need a new arrow function to act as it our callback and not use the functions that we already have ? walkDog(cleanKitchen(takeOutTrash)) I tried doing something like this , with the last function without a parameter since there is no next chore..It returned an error that the passed argument to walkDog is not a function ..and I checked the type by console.log(typeof cleanKitchen(takeOutTrash)) and it was undefined ..So this method only works for two chores maximum like this.. --> cleanKitchen(takeOutTrash) and the output will be following the order correctly 6:33 4) How can the function provide a value parameter ? one snippet of code that made me understand better is let prom = walkDog() // returns a promise object and store in prom setTimeout(() => {console.log(prom)}, 3000) /*which is going to make sure that the result of the promise is not pending , logging it without the timeout will output Promise { } which is also cool */ the output is going to be >> Promise { 'You walk the dog' } so we are just like passing the value to then handler like the following .. Promise {value}.then( value=>console.log(value)) ( searching different sites mainly FreeCodeCamp) our function walkDog is returning a promise object which can have there different results .. undefined: Initially when the state value is pending. value: When resolve(value) is called. error: When reject(error) is called. The .then() method should be called on the promise object to handle the value or the error of the promise. the parameters of then receive data from the Promise then(successFunc, rejectFunc) returns a promise If you are interested only in successful outcomes, you can just pass one argument to it. 7:22 5) Why returning cleanKitchen and not just calling it ? Because we want to return what the function returns so simply .. return what cleanKitchen returns cleanKitchen returns a promise and we want to returns that promise It just like storing the returned promise to const prom and then returning it like.. const prom = cleanKitchen() return prom we need a promise since we are going to attach the handler then to it

@TakiBARKAT-eh8rw 3 ай бұрын

thank you bro, you really helped me

@divyaanshuagrawal3383 3 ай бұрын

Bro i was having the same doubt as your 3rd point! Thanks for sharing!

@JW-uc6md 3 ай бұрын

thanks !

@hamodi20091 11 ай бұрын

Finally, I understand PROMISES. Thanks

@SaintHanappi 11 ай бұрын

Take out the trash "is really quick" => open the window/door - throw the trash - close. 🙊 .... Thank you! Getting closer to understand. (The value in the end is a bit "confusing", but I will make some studies and samples.)

@BroCodez 11 ай бұрын

async/await simplifies the process in the next topic

@anonymousguy6614 5 ай бұрын

Legend. Such a hard concept to grasp, and after watching your video and following along closely, I understand Promises now. Entertaining, imo funny, and educational video. You never disappoint me. Thank you so much. You're awesome!

@gokhanozdemir8970 8 ай бұрын

Your video made promises clear in my head. Thank you for your effort.

@altlalit 10 ай бұрын

It is the best explanation ever. Thanks

@Elizabeth_Calmau 2 күн бұрын

Why didn't I saw this video before? Now that's so clear! Thank you 🤗

@Granta_Omega 4 ай бұрын

2.5 seconds to clean the kitchen? Damn, that's a long time!

@haidermansoor4760 10 ай бұрын

The best tutorial on promises. Thanks mannn

@Isaac-ro1jl 15 күн бұрын

Using the ? operator makes simple stuff much easier, check it out : function task1() { return new Promise((resolve, reject) => { let completed = false; setTimeout(function () { completed ? resolve("task1 completed") : reject("didint complete task1"); }, 3000); }); }

@Pururin_Purin 10 ай бұрын

Honestly I find the "pyramid of doom" less confusing than promises

@pidli 9 ай бұрын

😂😂😂😂 same

@jeremyfrias7 8 ай бұрын

😅 It gets easier with a lot of repetition… It was hard to wrap my head around but just going back over and over and coding along simultaneously can & will do the trick.

@Ethan-Breitkreutz 8 ай бұрын

This is super helpful, last night was having trouble wrapping my head around this but this video really made it click! Thanks man!

@engenheirodesoftware 10 ай бұрын

Very good thank you.

@jktrivedi29 5 ай бұрын

Wow, after watching many videos finally i understood. Thanks.

@rbsfinger 9 ай бұрын

Bro, you rock. Thanks for the video!

@SuperDude101 11 ай бұрын

i just searched about this tomorrow and you uploaded it today what are the odds ;)

@mohantraju 8 ай бұрын

really helpful. Thanks

@sauzxa 3 ай бұрын

what a simple explanation after like 10 videos for that thx you bro 🙏

@hilmimusyafa 3 ай бұрын

BRO FINALLY I UNDERSTAND AFTER 5 VIDEOS AND COURSES

@mr.saiprasad5840 10 ай бұрын

The way of your explain is Awesome #BroCodez Thank You

@kianaparsi8223 24 күн бұрын

Fantastic, finally i got it🙏🙏❤️❤️

@renatocorreia1805 10 ай бұрын

THE BEST EXPLANATION

@mzedan2 8 ай бұрын

Thank you very much

@lillianirungu8180 6 ай бұрын

Wow thanks a lot. I was struggling to understand but now I do.

@mintymintfresh 2 ай бұрын

awsome explanation !!

@itzvaibhavkumar3029 5 ай бұрын

Man i love you sm i had such a hard time understanding callbacks and promises

@s21ekosn8 3 ай бұрын

thanks

@yy.u.i 7 ай бұрын

Thank you, it was very clear and simple.

@open2003 7 ай бұрын

You are awesome

@lambo-ca 7 ай бұрын

I finally fully understood. Thanks man.

@bordercut1 5 ай бұрын

sharp.

@oshadhaedirisinghe1455 5 ай бұрын

Thank you

@rajatsachann 7 ай бұрын

Youre a savior man!

@sekwayimokoena3225 10 ай бұрын

The best!

@J4nlks 6 ай бұрын

Yuuuhh, killed it mann

@beepboopitsjoop4678 11 ай бұрын

where was this when i was banging my head against the wall learning this ;.;

@BroCodez 11 ай бұрын

I was probably still recording it lol

@ShaileshKumar-re6yz 6 ай бұрын

Can you please explain the code you wrote inside the then() method. What does it do and why are we creating the arrow function with value parameter and how is it able to access the resolve value

@drewlee7435 4 ай бұрын

When you pass the value into the resolve, that value parameter is what gets sent to the ".then()" function (as a parameter) written at the end of the file. Just how promises work

@ОлександрКанюка-ч2ъ 7 ай бұрын

Thank you, it really helped me

@andrewchukwudumeje9413 6 ай бұрын

If the code is asynchronous why does the first reject prevent the other functions from being executed

@chomantsang3906 5 ай бұрын

Because it promises to return a value, but the next function depends on the value.

@sedhunique 4 ай бұрын

So basiclly, we created async to make code run parallely,... then we found out that it caused some errors,... so we again create promises to make the async code, run sychronously 💀

@TragicGFuel 3 ай бұрын

No, it seems you have no fundamental understanding of how javascript runs. It's not parallel.

@bryanquartey-papafio7628 Ай бұрын

@@TragicGFuel he was right at the last part tho it did make it run synchronously

@TragicGFuel Ай бұрын

@@bryanquartey-papafio7628 no he's misunderstood event based async with truly parallel async. I doubt he would know the difference between concurrent and parallel

@bryanquartey-papafio7628 Ай бұрын

@@TragicGFuel oh wait I see

@xXAngelmlXx 6 ай бұрын

I understood it, but you made it a little unclear than it should have. Using .then.then.then without returning anything would've been a little clearer maybe, but there are a few other ways.

@Ershaad-ss3uc 5 ай бұрын

OO LA LA

@rustyking23able 9 ай бұрын

I noticed some tutorials will create a variable equally a new promise kinda like this "var p = new Promise((resolve, reject))" ... in your example you returned promises, is there a preferred way or this situational ?