morning show where we try to become more
excited and confident about programming
by exploring all wisdom wild ideas and
having fun some viewers a few have
commented on the fact that I like to
omits semicolons from my JavaScript
instead of writing the same comment over
and over again I’d like to talk a little
bit about that today let’s get one thing
straight here before we continue I do
not recommend that you omit semicolons
nor do I recommend that you should use
them I will love you just as much if you
omit them like github does or if you use
them as terminating statements of never
lying like we do at Spotify if somebody
tells you that it is a general best
practice to use semicolons in JavaScript
that person is lying there is no central
authority setting best practices for
JavaScript as practice that’s what you
and your team decides is best practice
so what do you base that decision on
them well a lot of teams prefer to use
semicolons just well because it’s what
they ended up doing the team needed a
consistent rule for using semicolons or
not and they just opted for using them I
think that is a perfectly valid reason
consistency is very nice and important
other teams might use semicolons because
they might be switching a lot between AC
code base and JavaScript code base and
having semicolons makes the switch less
jarring and that’s an okay reason to in
my book context switching is expensive
and if we can make that easier and
that’s a good thing by now you should
have sense that there is a big hairy
butt coming up here but in my opinion
there is one invalid reason for using
semicolons and it is unfortunately also
a very common one and that is because
there are a lot of people while meaning
people going around spreading
misinformation and fear saying that
using semicolons
protects you from errors related to
automatic semicolon insertion we will
call those people wrong so in case
you’re new to JavaScript the language
has this feature called automatic
semicolon insertion often referred to as
a si automatic semicolon insertion does
what it sounds like it does if you don’t
add a semicolon at the end of a line the
interpreter will simply add one for you
while parsing your code mostly this
works but sometimes it results in some
very nasty errors like this one yeah
this is usually one of the first ones
that you run into when you start coding
javascript the first function here will
return for while the second one will
return undefined and that is because the
interpreter will interpret the code R by
adding semicolons like this do you see
how sinister this is almost everyone
agrees that automatic semicolon
insertion is a stupid feature it should
not be in JavaScript it is a super dumb
feature related to this there is a very
common advice given and that advice is
that you should not rely on automatic
semicolon insertion and to me that that
advised it I don’t think it makes sense
it would be perfectly good advice if the
automatic semicolon insertion could be
turned off but it can’t be turned off
the a si is there it’s it’s there to
stay it’s in the interpreter it’s in the
standard and it’s going to try to help
you and do it’s stupid things all the
time giving this advice kind of implies
that you can get rid of it somehow and
but you can’t let’s take a look
at the last function the one with the a
si R but ah here we have added a
semicolon at the end you know but
correctly
and this will still return undefined
because the interpreter will just do
this the semicolon will not help you
adding semicolons everywhere will not
absorb you from thinking about the ASI
not at all
this is JavaScript it’s a great little
language but the ASI that’s one of its
warts and you’re going to have to deal
with it you cannot semicolon it away as
a JavaScript programmer you cannot be
absorbed of your responsibility to
constantly think about the ASI just by
adding a semicolon rule to your lender
the only situation where having
semicolons everywhere will save you from
an ASI error is when you begin a line
with a parenthesis or a square bracket
by the way this example was sent to me
by
Fedora’s he is this brilliant Greek man
working at Spotify and he disagrees with
me vehemently on this issue
you should really follow him on Twitter
at 72 lines he’s awesome as you see here
the result is just unimaginable garble
I’m not even sure exactly how this is
messed up but adding a semicolon at the
end of the first line like this will
actually change the execution of the
code completely and that is square
brackets but it’s the same thing when
you start aligned with a parenthesis
like this and that will be evaluated as
this beginning a line with a square
bracket or a parenthesis are the only
cases that I know of we’re adding
semicolons will save you from asi errors
all the other possible asi RS will still
hit you even if you add semi-colons
everywhere you’re basically adding a
character to every single line in your
code base in order to protect you from
this case and in my personal experience
this is just not one of the common
insiders and when it arises it’s of
quite obvious what has happened again I
have nothing against people using
semicolons I just have a problem with
people saying that it’s a tool to
protect against ASI errors because it is
a terribly bad tool for protecting
against ASIS only learning how ASI works
will protect you from a hires by all
means use semicolons for consistency or
just because your team likes it that way
because it’s more C like or just because
you like how it looks or find it more
readable with semicolons but don’t buy
into the religion that it absolves you
from thinking about automatic semicolon
insertion that is just a false sense of
security the ASI is always with you and
you as a JavaScript programmer will
always need to be vigilant no matter if
you add semicolons or not I have one
more thing to say but I I need to show
you this isn’t it awesome I don’t know
if you can see it but this this is this
is an old cross stitch and this is
lechuck from Monkey Island made with the
fusible plastic beeps this is so awesome
this is made by Papa’s palü and I’m a
huge fan of him this video is running a
bit longer than I would like it to but I
I just want to finish up with one more
thing because I feel it’s important this
semicolon thing is an incredibly common
comment on my videos even on videos
where there is a obvious bug in my code
there are more people commenting about
the lack of semicolons than the I
think it’s kind of important in in the
workplace and and only internet to –
before before raising an issue to ask
yourself will raising this issue
actually add some value or am i raising
this issue just because it’s really easy
to have an opinion about it and I know
that it is very ironic to say this
considering that I made an entire video
about this issue but
this issue semicolons or no semicolons
it’s not important mandatory code review
that is something that is important
error logging is important continuous
integration that is important semicolons
not so much in the grand scheme of
things that’s all I had to say as usual
the next episode will be out next Monday
morning GMT time don’t miss out
subscribe and until next Monday stay curious