In this post I get into some patterns I try to use while programming. These patterns are observations I've made about myself recently while working...
For further actions, you may consider blocking this person and/or reporting abuse
Personally, my favorite way to do JavaScript switches is to isolate them to their own function. If you're doing a simple dispatch, a function is already an appropriate abstraction, and
return
gives you the ability to avoid thebreak
mess.Utilizing the switch statement also dodges the biggest drawback of the object literal: the location of the object. If you put the object literal in your dispatch function, you're creating the object every time you run the function. If you create the object once outside of the function, now your dispatch logic is in a different place than the actual dispatch call.
I wish JavaScript had a built in pattern matching construct, but a well used switch statement isn't all that bad.
Example with no object creation in the function:
I love this solution, very simple;
I usually do this:
This is how redux architecture works ;)
I like that
switch
versus the one I wrote. :DI recently discovered pattern matching via Scala and enjoyed using it!
Why not wrap the whole thing in one function. Use it as a closure to store the type data then return the switch function to access it?
Cool post ! :)
Love seeing these posts! I just recently used a switch in my code and didn't like the overall bulk the switch created. Nice ideas on how to clean it up!
As a personal preference I just try to avoid nesting in any form as much as possible because it really obscures the logic.
Say, this code snippet,
into:
or even:
Everything else looks fine but the nested turn ops.. not for me, clarity can go a long way over terse for the sake of others. Besides there are alternatives to nested conditionals. Boolean array .every or .some spring to mind.
Clever! Gonna remember this one
Your most welcome 😄, this is functional programming at it's finest. The only thing I don't like is the need to return the result by lambda. I haven't tried it but perhaps the
Boolean
constructor could sit whereisTrue => isTrue
is currently? I am afk so can't test.This sentence went "swoosh" over my head.
I also had to google what a lambda was - had never heard that name for an anonymous function before (but I'm an autodidact which could explain it..) 😂
Could you elaborate in an ELI5 way? :D
3. One loop two arrays
Is reduce really necessary here? Wouldn't it be so much clearer to do this with a
forEach
?5. Nested ternaries
The same flow you used in the ternaries can be applied to the
if
statements:And if you used the same flow as in your
if
statements but with ternaries, they'd also look weird:Also, I find ternaries formatting to be more readable this way:
I think reduce is nicer because it's always clear that an
Array.reduce
constructs "something" from an array. The whole statement includes everything you need to know (i.e. the final argument is the base value) as opposed to declaring the arrays before the loop. No need to look outside the reduce for answers since it's all there.Reduce can be a little intimidating in the beginning but once you get the hang of it it's wonderful and makes a lot of sense.
So it's better because you can put it in a single statement, even though you now have to address the arrays as
array[0]
andarray[1]
instead of by name?You don't! You could actually do this instead:
I've spread the array in the return statement because I wasn't too fond of the push along with having to return the two arrays.
Another one, using an object instead of two arrays would be:
Which in my opinion is probably the easiest one to read.
Which is how
reduce
is meant to be used, and why it is needed in functional languages that deal with immutable data. Otherwise you are just abusing it as a loop construct to feel functional.But I wouldn't recommend this style in Javascript, because arrays are not linked lists and this becomes O(n2).
I don't have a computer science background so what you're referring to is not something I can easily relate to. I have a vague idea of the concept of linked lists, but I don't understand the big O notation (entirely new concept to me).
Do you mean that it's less performant than needed? Because I'm creating a new array which contains two arrays both of which will have to be looped due to using the spread operator as opposed to a push (which would not need to loop the whole array)?
Sorry if I'm not very clear, I'm simply not very good with these concepts and I'm genuinely interested in understanding what you're saying.
Update: Ok, I think I understand now.. You're saying that my solution with the spread operator will decrease in performance for each value in the exampleValues array, which is a bad practice. And it's O(n2) (opposed to O(n)) because I'm doing it twice?
O(n2), not O(n2). As in - O(n*n). As the array get bigger, the spread operator takes more and more time to perform because it needs to copy more values, as opposed to
push
which only needs to add one value (and sometimes increase the size, which takes longer - but it doesn't do it on eachpush
)I'm aware, I just don't know how to do it on my keyboard. And yes, I do realise there's a major difference and it shouldn't be trivialised..
Anyway, thanks - I learned something new today :)
dev.to does it for you with the
^
operator - soO(n^2)
becomes O(n2).HA! I posted the almost the exact same else-if logic before realizing you had!
Personally, I don't like the nested ternary conditions.
Instead of the nested
if..else
, I would prefer the "Early assignment" like "Early Exits"Nice post!
Re #1: Rubocop calls them "guard clauses" and I tend to prefer that style as well.
But if there are only two branches, I sometimes prefer the symmetry of
if / else
. Especially whenif
is an expression (as it is in Ruby).Either way, IMO it's usually clear enough when input validation is being done, however it gets written. It's one of those places where obscuring the intent takes real talent :P
Re: #2: agree with @nepeckman that putting the switch statement in a function is usually a good option. Especially if multiple cases map to the same output value, because there you can use switch fallthrough to "stack" the tests and avoid repeating yourself.
Re: #3:
reduce
(fold) is so powerful 😍...map
andfilter
can both be written in terms of it, and many more things as well. Many "indexed" loops can be translated into a function folded over a range of integers.Also, I haven't seen it formalized, but it seems like a lot of tail-recursive code can be translated to "reducer style" as well -- it's a good option if the inputs can be easily generated as some sort of collection.
If the fold implementation allows early termination (a la Clojure's reduced, it becomes even more useful.
Oh yeah, in case you haven't seen it in action, you might be interested to know that a side-effect-free series of
map
calls can be refactored similar to your #3. map distributes across function composition, soThe latter form only walks the collection once, obviously. You can compose the functions manually or borrow
compose
from a library like Ramda.Part of our coding standard is no acronyms (with a very few specific exceptions for industry terms). It is amazing how much easier it is to read code from 5+ years ago when it isn't littered with little three letter shibboleths.
I think nesting ternaries makes things more difficult to change later without scratching your head. The linked article says it simplifies the conventional
if
but it doesn't go all the way:
At this point the
if
and the ternary are nearly identical, with the exception that theif
statement blocks can contain anything they like without breaking the layout. Imagine if instead of returning a simple value they were all returning a long string or a calculation? I mean, you can say that these sorts of things should be factored into their own functions, but that's true of both techniques.There is a very unfortunate drawback of using a function for "if" or ternary... both branches are always evaluated and that often means dereferencing null or undefined...
Early exits keep indentation sane which contributes a lot to readability.
Nested ternaries are great and very clear if you lay them out like:
so the structure of each line is exactly the same.
(Don't try this in PHP by the way - you need parens to fix the broken associativity).
You're right. I have found it is exactly easy to understand the ternaries because the priority level is default satisfying what I want it to be. But
One loop two arrays
I don't agree. I code the following code and it is more elegant:I love nested ternaries, shortens the code. A real world example, simple Vue-router meta controlling;
cond1 ? true : cond2 ? true : false
is the same as
cond1 || cond2
I really appreciate and identify with this article.
But... Not the nested ternaries. The example used as the "bad nested if" feels to me like those commercials for cracking eggs and how no one can do it (meaning, it's actually easy, but we want to sell you a thing)
First, let's kill the unneeded semicolons, because, yuck. Second, reverse the first logic and use
else if
for the second and you have yourself some pretty simple logic that can also be multiple lines long... but... for the sake of this example we don't need curly braces either. So apples to apples if code would be below. Honestly, the nested ternary functions I've seen are a HUGE mess, not at all as simple as the example provided. Especially while returning JSX and returning blocks of JSX-HTML...shudderMulti-line Version
When using reduce, I prefer to always return a new pure array rather than pushing to an existing array. Keeping reduce stateless has resulted in less debugging for me.
I'm sorry, but if you like nested ternaries you are either a bad man or someone who didn't have a 4 or 5 nested ternary that made you scream with pain. Or both :D
😅
I haven't done 4 or 5 nested. That seems a bit much lol
Well, I have PTSD with using ternaries. I once did some work in Jasper Reports and their scripting language used only ternaries. Now every ternary that is longer than 1 line (max 2 at the most) gives me the creeps and is an instant code smell for me
Nested ternaries can be tricky for their operator not having the same priority between programming langages :
Also using spaces or multiple lines may mislead the programmer, suggesting priority :
To me, it is always better to use parenthesis, on one line of code. If the line goes too long you should use variables (as in pattern 4 "No 'foo' variables") :
Still my preference goes to a non nested if/elseif/else blocks (i find it a lot clearer) :
I use mostly Ada and very sparingly JavaScript, but...
(1) I agree with the "no foo" suggestion (although when I am really in a hurry I throw in a "Tmp" with the idea of choosing a better name later...). I always try to use fully readable names for my variables and functions.
(2) About the nesting of ternary operator, my preference goes to the "ternary Ada style," similar to the ?: but with full verbose "if", "then", "else" and, if needed, "elsif" :-) oh, yes, and "case..when" :-)
These patterns are so useful in day to day work!
In the 'one loop two arrays' pattern for partitioning I like to emphasize what is the essential, minimal difference in each condition. In this case, it's really just 'what array do I append to?'
For nested ternaries we can use self-executable loops:
{ (() => {
if(x) {
//do something...
console.log(''x')
}
if(y) {
//do something...
console.log(''x')
}
if(z) {
//do something...
console.log(''x')
}
}
)()
}
Are you thinking about specific programming patterns, when you are programming? Like "Oh, I gotta use 1. Early exits right now." 😀
:D
Definitely not, just things I noticed I do sometimes.
Instead of switch to object literal I suggest the facade pattern. Going with facade pattern, your IDE will be able to resolve function definition. If this object resolution grows in complexity it will be harder to understand why this generic function refers to and only your debugger can help you.
The details of this would be an interesting topic for a follow-up article.
Googled and found this:
I like it.
The Early Exits I know them as "Quick Fails" and its the best patter I learned recently.
I like that name also
Awesome article mate 👌
I liked the first two and use very often.
I kind of feel nested ternary is more confusing though mileage varies person to person.
Great post! We both use the first concept you mentioned in the post. I'll explore the others and see how I can incorporate them also.
Thanks!
Where are these terms?
Such an incredible idea is in 'bifurcate'
Omitting the else and else ifs when you do the early return always seems dangerous.
hi,
someone can give me advice which book about programming patterns to buy ? I'm interested in this.
thanks
It's very relatable, have been doing almost all of them in my code (except the two arrays pattern, which is a great idea as well).
JavaScript X.X