DEV Community: Jens K Vyff

Checking if a Variable Exists

Jens K Vyff — Fri, 13 Dec 2019 23:03:26 +0000

For an interview this week, I was doing an online technical interview and under pressure, I quickly used a check to see if a value existed.

if (x) {
    numberArray.push(x);
};

However, the data I was filtering contained values of 0 and null that needed to be treated differently and intentionally undeclared values that I would usually catch in my own code base or with a linter.

The rules I was trying to filter to could be summarized a such:

const v = 'abc'     // exists
const w = 0         // exists
const x = null      // nope
const y = undefined // nope
// const z          // nope

My first attempt was equivalent to:

if (x == true) { 
    //Do stuff
}

'x' is cast to its boolean equivalent type, but 0 in javascript is the only number that casts to false.

The second area where it deviated is for cases like 'z' where a variable is unassigned or undefined and a comparison is being made, JavaScript will error out. This is not a great user experience.

Here are the results of a few of my tests until I eventually arrived at a way of checking a values existence that I needed.

Tests

The quick and dirty with some pitfalls

console.log(v ? 'exists': 'nope'); // exists
console.log(w ? 'exists': 'nope'); // nope
console.log(x ? 'exists': 'nope'); // nope
console.log(y ? 'exists': 'nope'); // nope
console.log(z ? 'exists': 'nope'); // ReferenceError: z is not defined

Captures 0, but now also null values and still errors out

console.log(v !== undefined ? 'exists': 'nope'); // exists
console.log(w !== undefined ? 'exists': 'nope'); // exists
console.log(x !== undefined ? 'exists': 'nope'); // exists
console.log(y !== undefined ? 'exists': 'nope'); // nope
console.log(z !== undefined ? 'exists': 'nope'); // ReferenceError: z is not defined

Closer, but now we are casting types again, and still doing the comparison that breaks on undeclared variables

console.log(v != null ? 'exists': 'nope'); // exists
console.log(w != null ? 'exists': 'nope'); // exists
console.log(x != null ? 'exists': 'nope'); // nope
console.log(y != null ? 'exists': 'nope'); // nope
console.log(z != null ? 'exists': 'nope'); // ReferenceError: z is not defined

The recommended safe way for most applications

console.log(typeof v !== 'undefined' ? 'exists': 'nope'); // exists
console.log(typeof w !== 'undefined' ? 'exists': 'nope'); // exists
console.log(typeof x !== 'undefined' ? 'exists': 'nope'); // exists
console.log(typeof y !== 'undefined' ? 'exists': 'nope'); // nope
console.log(typeof z !== 'undefined' ? 'exists': 'nope'); // nope

Extended version of the recommended method for the filter I needed

console.log(typeof v !== 'undefined' && v !== null ? 'exists': 'nope'); // exists
console.log(typeof w !== 'undefined' && w !== null ? 'exists': 'nope'); // exists
console.log(typeof x !== 'undefined' && x !== null ? 'exists': 'nope'); // nope
console.log(typeof y !== 'undefined' && y !== null ? 'exists': 'nope'); // nope
console.log(typeof z !== 'undefined' && z !== null ? 'exists': 'nope'); // nope

TLDR:

use (typeof value !== 'undefined')

if (typeof value !== 'undefined') { 
    //Do stuff
}

Bonus:

While every number but 0 casts to true, booleans cast to a number are:
true -> 1
false -> 0
This leads to fun cases like:

-1 == true;          // false
-1 == false          // false
-1 ? true : false;   // true

This is because after casting to types the equivalent expressions are:

-1 == 1;             // false
-1 == 0;             // false
true ? true : false; // true

Reference

*Bonus from Stackoverflow

Reset or sync local branch to a remote repository

Jens K Vyff — Fri, 15 Nov 2019 05:38:26 +0000

Header image: “Git Branches” by Atlassian under CC BY 2.5 Australia

You want to contribute to an opensource project, but you want to work from the latest copy of the software and the fork you have is out of date, how do you sync your local copy with the upstream project or your origin fork.

Lucky git can do all of that, so let me show you how.

TLDR:

# Need to remember the command and have your upstream remote already?
git fetch upstream
git checkout master
git merge upstream/master
git push origin master

# If you are a madman or know that you local repo didn't change
git checkout master
git pull upstream master
git push origin master

Using the Command Line to sync your fork to the original repo on Github

First, the easiest, cleanest, and easiest to understand is generating a clean fork.

Cloning

git clone git@github.com:YOUR-USERNAME/YOUR-FORKED-REPO.git

If you already have a fork and you want to update it, the steps a slightly different.

Adding Remote

# Check if you have a remote to the original repo. If not, it should return origin.
# Optionally add -v flag for more info
git remote
> origin
# If you don't have a remote to the original repo, add it with  
git remote add upstream git://github.com/ORIGINAL-REPO-USERNAME/REPO-YOU-FORKED-FROM.git

Update from Original Repo

Now you have added a remote that points to the original repo, much like how you usually interact with the fork in your Github. Time to get the latest update.

You have a many options here fetch/merge, fetch/rebase, fetch/reset --hard, or pull.
So let us go through and see their tradeoffs.

For fetch/merge(The recommended method by Github)

# Fetches copy of repo from upstream and creates a new commit that is the merged
# result of combining commits from the upstream version and your local copy.
git fetch upstream
git checkout master
git merge upstream/master

For fetch/rebase(Try to only use in private repos)

# Resets your local master branch to that of upstream and then rewrites 
# the changes over your local master branch.(Changes history of commits)
git fetch upstream
git checkout master
git rebase upstream/master

For fetch/reset --hard

# This command will destroy local changes to your current branch and your 
# local copy will reflect the original repo.(Removes local work)
git fetch upstream
git checkout master
git reset --hard upstream/master
git clean -f -d

For pull

# A pull request performs a `git fetch` and then `git merge FETCH_HEAD`
# Good for writing to a clean branch or repo. (but can be conflict prone otherwise)
git checkout master
git pull upstream master

Pushing to forked Repo

You may now push the local copy to your fork or simply begin working again.

# Push local changes to your origin fork
git push origin master
# or 
git push
# Sometimes rebasing will require you to force the changes when pushing to your fork. 
# In that case, you will need to force the push.
git push -f origin master

Extra Tips

If you are using a method that discards your local changes, these two commands are helpful to store your changes for later:

# To store your changes
git stash
# To get the changes back
git stash pop

If you have just fetched and want to know the difference between what you fetched and your local copy before merging:

# Returns any differences between two branches
git diff remotes/upstream/master master

If you want to see where your copy of upstream master is stored:

# Returns all branches, including remote tracking-branches
git branch -va

All done :)

Resources

Reduce Exposure to What You Can't Control... When You Can

Jens K Vyff — Sat, 13 Jul 2019 19:48:32 +0000

I just want to ask the question of why what we write can be perfectly performant and still be trash.

There is a concept in system design called high availability. Frequently used to provide an expectation for a level of the system performing as expected is the shorthand "five 9's" or 99.999% uptime, about. Many fields shoot for this goal of system availability or even higher(hospitals, airline equipment, and satellite software).

Wow, what a dream, but what about WebDev. I want to be able to write code and perform at those level, but i'm working in distributed hardware(servers, routers), with distributed software(packages, links, libraries). Let's start with the data center where our site is hosted.

https://hostingfacts.com/average-hosting-uptime-study/

Whoops, the highest average was just four 9's and we haven't even written any code yet.

At least google handles their own hosting and has it figured out.

G Suite

@gsuite

Google Calendar is currently experiencing a service disruption. Please stay tuned for updates or follow here: goo.gl/NOZTZ

14:39 PM - 18 Jun 2019

109 209

..oh no

Chip Wolf

@chipwolfuk

@gsuite

14:43 PM - 18 Jun 2019

0 36

Looks like G-Cal was down for for a little over three hours, that puts it at three 9's for the year.

We as web devs are used to relying on so many dependancies we can't even properly estimate how many lines of code are running.

One Dev Casey Muratori tried to figure out how much code has to be brought in and used in a typical web stack from a few years ago and stopped at 56 million lines. Granted, one wouldn't use all the functions and methods brought in through this stack, but it does make some issues difficult or impossible to actually test.

https://www.youtube.com/watch?v=kZRE7HIO3vk

My point is not that we shouldn't use these technologies. But just be aware of what you are bringing in to your stack, try to limit the code you bring to a project if you don't understand how it runs at a deeper level, because as a web dev you are already at four 9's or worse assuming your code is perfect.

Resources

Ruby Code Golf: Tips to Squash Character Counts

Jens K Vyff — Tue, 04 Jun 2019 15:35:54 +0000

So you want to write succinct Ruby code that accomplishes magic in 40 characters, but maybe you can squeeze it down to just 39. This is the wonderful world of code golf. Write code that solves a problem in as few characters as possible.

Sorry linters and good code convention in general. But i'm trying to write a program that can sit in 50 Bytes of memory comfortably.

Get Rid of Bytes

Lets dive into a few common use cases where you could be doing the same work in fewer characters.

Methods

We are used to methods like this.

#(22 bytes)Beautiful, legible, and far too many bytes.
def add1(x)
    x + 1
end

#(15 bytes)Method name is now one char and we lost formatting.
def d x
x+1
end

#(12 bytes)You have probably used this compact form for a short method.
def d x{x+1}

#(10 bytes)But we can do better with a lambda object.
d=->x{x+1}

Note: Lambdas aren't called like other methods, you have the options:

d.call(4) => 5
d.(4) => 5
d[4] => 5

So we save 2 bytes defining with lambda and variable
d=->x vs def d x
but we lose a byte for our shortest call
d[x] vs d x
The number of calls and variables in our program will change wether we use a method or lambda.

Looping

Quick tip: if assigning a parameter for your loops, it is often shorter though still valid to use < or > as opposed to ==.

There are many ways to create loops in ruby, but the most useful are:

.map when altering data to container of the same size
.times when one knows the number of times to perform a method
.upto for cases where I would use a .times method on a string

#upto example
'1'.upto('3'){puts "cat"}
#or
'a'.upto('c'){puts "cat"}
> cat
> cat
> cat
=> nil

Printing

Ruby helps us out here as methods have an implicit return value, but that will not always be enough to get what we want. Upon seeing the output methods print, puts, and p it may seem like p is the obvious choice.

However, print, puts, and p are not alias' for one another and while p is a good choice to default to, sometimes it is faster to use one of the others if it's default output for your datatype is in the format you want.

#calls to_s on the object
print 1,2,3
> 123 => nil

#calls to_s on the object and newline after an element
puts 1,2,3
> 1
> 2
> 3
> => nil

#calls Also adds newline, but calls inspect, so you return the actual class of an object
p 1,2,3
> 1
> 2
> 3
> => [1, 2, 3]

Tip: Because of this, printing a symbol with print or puts instead of a string can save a byte.

Also useful in printing are the escape sequences for strings in double quotes.

\" – double quote
\\ – single backslash
\a – bell/alert
\b – backspace
\r – carriage return
\n – newline
\s – space
\t – tab

Extras

Try t, *m, b = [1,2,3,4,5] if you want to use many parts of an array
- t => 1
- m => [2,3,4]
- b => 5
Save a byte
- calling chars using a question mark like ?, instead of ','
An alias for .join() is \* so d.join(',') could become d\*?,
Use -[nil] or -[p] in place of .compact
Check array uniqueness with a==a.uniq
Find if character is included in an array

n = [1,2,3,4,5]
#(5 bytes)use the triple equals
n===3
> true

#shorter than the alternatives

#(11 bytes)
n.member? 3
> true

#(12 bytes)
n.include? 6
> false

Challenge

Using these techniques, I was able to get on the leaderboard of a fun golf challenge site. Beat my best if you can.

(Sorry code golf site for the double publish... forgot to put a name.)

Resources

https://codegolf.stackexchange.com/questions/363/tips-for-golfing-in-ruby?page=2&tab=Votes
https://medium.com/ruby-golf/ruby-golf-cheatsheet-eb27ec2cdf60
https://www.garethrees.co.uk/2013/05/04/p-vs-puts-vs-print-in-ruby/
http://golf.shinh.org/p.rb?pascal+triangle