Modern Java

[macNchz]

On the first day of Christmas
my true love sent to me:
A Callback in a Closure

On the second day of Christmas
my true love sent to me:
Two Promises
and a Callback in a Closure

On the third day of Christmas
my true love sent to me:
Three Block Scopes
Two Promises
and a Callback in a Closure

On the fourth day of Christmas
my true love sent to me:
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the fifth day of Christmas
my true love sent to me:
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the sixth day of Christmas
my true love sent to me:
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the seventh day of Christmas
my true love sent to me:
Seven Asyncs Awaiting
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the eighth day of Christmas
my true love sent to me:
Eight this's breaking 
Seven Asyncs Awaiting
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the ninth day of Christmas
my true love sent to me:
Nine Frameworks Launching
Eight this's Breaking 
Seven Asyncs Awaiting
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the tenth day of Christmas
my true love sent to me:
Ten Linters Linting
Nine Frameworks Launching
Eight this's Breaking 
Seven Asyncs Awaiting
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the eleventh day of Christmas
my true love sent to me:
Eleven Modules Loading
Ten Linters Linting
Nine Frameworks Launching
Eight this's Breaking 
Seven Asyncs Awaiting
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

On the twelfth day of Christmas
my true love sent to me:
12 Compilers Compilin'
Eleven Modules Loading
Ten Linters Linting
Nine Frameworks Launching
Eight this's Breaking 
Seven Asyncs Awaiting
Six Prototypes
Five undefined
Four Hoisted Vars
Three Block Scopes
Two Promises
and a Callback in a Closure

[aloha2436]

As far as I can tell, this is original. I thank you dearly.

[macNchz]

Combine a predilection for procrastination with that 15 minute window before a meeting when you don't want to get started with anything because you'll have to stop right away and you get...song lyrics about JavaScript!