This document introduces Seq, a library for Node.js that provides a cleaner way to handle asynchronous flow control and parallel execution. It summarizes Seq's installation, basic usage with examples, handling errors, nested execution, and more advanced features. Seq allows asynchronous functions to be executed sequentially or in parallel using methods like seq(), seqEach(), and parEach() to simplify complex asynchronous code and avoid "boomerang code". The document provides resources to learn more about Seq and asynchronous programming.

1. PRESENTING:
SEQ

2. ABOUT ME
Who I am: Douglas Muth
How to contact me: dmuth@dmuth.org / @dmuth
What I do: Software Engineer ...mostly.

3. THE PROBLEM
Flow control in node.js.
Node.js is a callback-heavy language.
Often, it looks like this:
d.ur(SLC ..,fnto(ro,rsls {
bqey"EET ." ucinerr eut)
i (err {
f !ro)
d.ur(UDT ..,fnto(ro,rsls {
bqey"PAE ." ucinerr eut)
i (err {
f !ro)
d.ur(ISR ..,fnto(ro,rsls {
bqey"NET ." ucinerr eut)
/ O Gd wy
/ h o, h?
}
}
};
)
}
};
)
Also known as "boomerang code"!

4. SEQ 101
INSTALLATION
$nmisalsq
p ntl e
That was easy!

5. SEQ 101
USAGE
vrsq=rqie"e";
a e
eur(sq)
sq)sqfnto( {
e(.e(ucin)
d.ur(SLC ..,ti)
bqey"EET ." hs;
}.e(ucinrsls {
)sqfnto(eut)
d.ur(UDT ..,ti)
bqey"PAE ." hs;
}.e(ucinrsls {
)sqfnto(eut)
d.ur(ISR ..,ti) / Pet set
bqey"NET ." hs; / rty we!
};
)
"this()" is the callback which goes to the next block of code

6. SEQ 101
WHEN THINGS GO WRONG
sq)sqfnto( {
e(.e(ucin)
d.ur(SLC ..,ti)
bqey"EET ." hs;
}.e(ucinrsls {
)sqfnto(eut)
ti(e Err"hk tig u altl")
hsnw ro(Sae hns p
ite);
}.e(ucinrsls {
)sqfnto(eut)
/ Ti wl nvrrn
/ hs il ee u
d.ur(ISR ..,ti)
bqey"NET ." hs;
}.ac(ucinerr {
)cthfnto(ro)
/ Igtti!
/
o hs
};
)

7. HOW TO SEQ
IT'S A TRAP!
sq)sqfnto( {
e(.e(ucin)
d.ur(SLC ..,ti)
bqey"EET ." hs;
}.e(ucinrsls {
)sqfnto(eut)
sq)sqfnto( {
e(.e(ucin)
/ D smtig
/ o oehn
}.e(ucin){
)sqfnto(
/ D smtiges
/ o oehn le
/ Ti wntg t teotrSq
/ hs o' o o h ue e
ti(;
hs)
}.e(ucin){
)sqfnto(
/ Ti gt cle b acdn
/ hs es ald y ciet
};
)
}.e(ucinrsls {
)sqfnto(eut)
/ Ti wl nvrrn
/ hs il ee u
d.ur(ISR ..,ti)
bqey"NET ." hs;
};
)

8. SEQ 101
SAFE NESTING OF SEQ
sq)sqfnto( {
e(.e(ucin)
d.ur(SLC ..,ti)
bqey"EET ." hs;
}.e(ucinrsls {
)sqfnto(eut)
vrc =ti;/ ti( b ayohrnm.
a b
hs / hs) y n te ae.
sq)sqfnto( {
e(.e(ucin)
/ D smtig
/ o oehn
}.e(ucin){
)sqfnto(
/ D smtiges
/ o oehn le
/ Ti wntg t teotrSq
/ hs o' o o h ue e
c(;
b)
}.e(ucin){
)sqfnto(
/ Ti nvrgt cle
/ hs ee es ald
};
)
}.e(ucinrsls {
)sqfnto(eut)
/ Ti gt cle
/ hs es ald
d.ur(ISR ..,ti)
bqey"NET ." hs;
};
)

9. ADVANCED SEQ
vrf =rqie's)
a s
eur(f';
vree =rqie'hl_rcs'.xc
a xc
eur(cidpoes)ee;
vrSq=rqie'e';
a e
eur(sq)
Sq)
e(
.e(ucinse1){
sqfnto tp(
ee(wom' ti)
xc'hai, hs
}
)
.a(ucinse2wo {
prfnto tp(h)
ee(gop '+wo ti)
xc'rus
h, hs;
}
)
.a(ucinse3wo {
prfnto tp(h)
f.edie_flnm,'si' ti)
sraFl(_ieae aci, hs;
}
)
.e(ucinse4gop,sc {
sqfnto tp(rus r)
cnoelg'rus '+gop.rm);
osl.o(Gop:
rusti()
cnoelg'hsfl hs'+sclnt +'bts)
osl.o(Ti ie a
r.egh
ye';
}
)
;
Order of execution is as follows:
step1()
step2() and step3() are executed in parallel
step4() ONLY when step2() and step3() complete

10. EVEN MORE SEQ
Process an array of elements:
forEach()
seqEach()
parEach()
Play around with "this":
this.stack
this.vars
this.into(key)
this.args
Not for the faint of heart, and WAY beyond the scope of this
presentation.

11. FURTHER READING
The Seq repo:
https://github.com/substack/node-seq/

12. ON THE WEB
https://github.com/dmuth/nodejs-presentations
Feel free to clone and add your own presentations based off of
template.html!

13. QUESTIONS?