Javascript Promise chaining

Hi there here is the third post of Javascript/NodeJs callback.

We have an async task with Promise:

[gist https://gist.github.com/vanduc1102/d7c84cd605edf8d0faf1fb620556ba5f]

Create tasks function:

[gist https://gist.github.com/vanduc1102/d07c13973a4c3cda3973b12f6619f1b9]

Promise.all

execute all the promises at the same times, and resolve when all of the promises resolved

[gist https://gist.github.com/vanduc1102/8b85ee8ce42d23fb49ae9d165bb19794]

and reject when any of the Promise was rejected:

[gist https://gist.github.com/vanduc1102/09a90b3923ca1ba3d5d72630958e950a]

Promise.race

The Promise.race(iterable) method returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.

[gist https://gist.github.com/vanduc1102/21ff8e6900ebfb1824c965fb1d654291]

Sequence Promises

Sometimes we need to do the jobs in sequences.
[gist https://gist.github.com/vanduc1102/5264a38f20f54d04360a191e53c5e7e3]

For promise functions with multiple parameters

[gist https://gist.github.com/vanduc1102/b15f3f2ff5733ebbc467464e96cdf2ea]

 

Online editor

https://repl.it/@vanduc1102/sequence-promises

 

 

Javascript Callback Hell and Promise

The last article with the callback, we use callback function to solve the issue with asynchronous in Nodejs/Javascript.
[gist https://gist.github.com/vanduc1102/5e2e7cea325e628ad91fa11f6170d7a1]

But life is not that easy; sometimes a task needs more effort to be done.
Let assumed our task splits into three tasks now:
[gist https://gist.github.com/vanduc1102/b63a58ef1751d231d9111339be09df46]

In other to finish a task we need a callback hell (http://callbackhell.com/):

[gist https://gist.github.com/vanduc1102/f679b6039afd1ba893b310ace5b93e87]

Gather all snippets together:

[gist https://gist.github.com/vanduc1102/b22979ea867d47777e413c0831402fef]

Result:



In reality, a task may need more and more sub-tasks, the nesting will be super crazy.

Now we speak about Promise. Let convert our simple task from callback to promise
[gist https://gist.github.com/vanduc1102/523f1ffb2dccb9cc80f49de2d79e5611]

And then we will use Promise chaining to solve the callback hell issue.

[gist https://gist.github.com/vanduc1102/0b03c51edd629f05e1ddec95c7a288a8]

The result:



 

Conclusion: To be honest I don't see my example has a clear explanation about Promise over Callback Hell, but you have to trust me, you will see Promise very helpful later.