From Callback Hell to AsyncHeaven – Promises!

A Play in Three Acts:Inferno, Purgatorio, and Paradiso

THE ROAD TO HELL IS PAVED WITH GOOD INTENTIONS

Act I: Inferno

Our Journey Begins

Focusing on the Main Code

The Good and the Bad

SimpleReadableDebuggable

Holds the Thread!Not Async!

SO HOW DO WE RELEASE THE THREAD?

Callbacks!

CALLBACKS

Good Intentions

Looks Good…

Doesn’t Look to Bad…

The Pyramid of Doom!

Our Code, In Hell

In Callback Hell, There are no Loops!

BUT I PROMISE – IT GETS BETTER

Act II: Purgatorio

Promises Instead of Callbacks

Chaining Promises

Easy Concurrency

ES6!

So How Do We Write promisedOpen?

Yes, But How do Promises Work?

• I don’t know

• And if I try to understand, my head hurts

• I just learn to accept it

Generalizing promisedOpen Across All Node Functions

ES6!

So Where Does This Take Us?

Ugh…

Still no loop

PROMISES MUST BE KEPT –ONWARD TO ASYNC HEAVEN!

Act III: Paradiso

BUT LET’S YIELD TO A LITTLE DETOUR

Generator Functions

Iterator Protocol

We could have done it like this…

ES6!

But the ES6 compiler does it like this…

Bi-Directional Protocol

THIS IS WHERE IT BECOMESMIND-BOGGLING

Can We Fulfill The Promise?

Sure!

So What About This?

No Problem!

Let’s Generalize

And… Async Heaven!

Compare

The Future

SO…

Epilogue

From Callback Hell

To Async Heaven

Our Journey is Complete

Thank You

https://github.com/giltayar/callback-to-async-presentation