DEV Community

Cover image for 5 ways to refactor if/else statements in JS functions

5 ways to refactor if/else statements in JS functions

Sylwia Vargas on November 16, 2020

In this blog post I will present 5 ways to declutter your code getting rid of unnecessary if-else statements. I will talk about: default paramet...
Collapse
 
bugb profile image
bugb

Suppose you have a code like this:

function foo(arg) {
  if (arg === "a") return 1
  if (arg === "b") return 2
  return 3 //default value
}
Enter fullscreen mode Exit fullscreen mode

You can use something likes this instead of the example above or switch case:

const mapping = {
  a:  1.
  b:  2,
}
function foo(arg) {
  return mapping[arg] || 3;
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sqlrob profile image
Robert Myers

Personally, I'm a little torn on this pattern. It's compact, and I've definitely used it.

But, IMHO, it increases the cognitive load of the code, you now have two places to look for what it's doing.

Collapse
 
eecolor profile image
EECOLOR

it increases the cognitive load of the code, you now have two places to look for what it's doing

For that reason in some instances I use this:

function foo(arg) {
  return (
    arg === 'a' ? 1 :
    arg === 'b' ? 2 :
    3
  )
}
Enter fullscreen mode Exit fullscreen mode

or this:

function foo(arg) {
  return {
    a:  1,
    b:  2,
  }[arg] || 3
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
_hs_ profile image
HS • Edited

And performance impact. Using a map (object whatever the name) should introduce indexing operation in the background. On the other hand what if arg = null or arg = 123 or so? You need to handle all the cases instead of having simple switch with the default. Or even just using if's until you actually need more than 3 cases.

Thread Thread
 
rasmusvhansen profile image
rasmusvhansen • Edited

I doubt there is any real world performance issue here. And as soon as you have more than 2 cases, this is much more readable than a bunch of if statements.

Regarding handling arg=null or arg=123, I don't think I see the issue.
That is handled by the

 return mapping[arg] || 3;
Enter fullscreen mode Exit fullscreen mode

part.

Thread Thread
 
_hs_ profile image
HS • Edited

I highly doubt that using objects instead of switches and ifs has same performance. I'm not limiting it to this scenario but talking about generic overview why should one avoid switches and ifs in favour of objects or hash maps. Reason I'm asking is because I know for a fact that compilers (including JIT ones) and maybe some interpreters have really good optimizations which can even remove branching in some cases but I have no idea would such thing kick in for objects in JS. I know that c++ compiler since 2017 or so has really good optimizations that can turn generics, branching, hahsmaps into few instructions all together. There was a nice conf were, I forgot his name, wrote code on left side and on the right there was assembly outout. I also know JIT in Java will sometimes kick in an replace some of your code with shorter instructions than on first complie. Question is will such things be done by WebKit or others for JS.
Reagarding the safety again it's about generic thing not thi particular piece. It's much easier to have switch with default case and even shorter than objects and relying that || will not be forgotten

Thread Thread
 
rasmusvhansen profile image
rasmusvhansen

I think we are both right here.
You are right that there probably is a difference in performance.
And I am right that in the real world it will make no difference*.
I learned to always prefer readability and then profile if something is slow. It is usually not what you think that is slowing you down.

*Except in that 0.001% weird edge case

Thread Thread
 
xtofl profile image
xtofl

Fyi . The c++ tool mentioned would be godboldt.org.

Collapse
 
johnylab profile image
JoΓ£o Ferreira • Edited

I like too use mapping objects for everything, but never put a default inside the function. So all my attention is driven to the object. If the function doesn't find a value in the object, it does nothing and returns null, if needed a value.

Thread Thread
 
johnylab profile image
JoΓ£o Ferreira

"too" was mistype, but let it be

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Yeah, it's definitely less "user-friendly" or "beginner-friendly". Coming from Ruby, it gave me chills but also I was really excited for the shorthand properties so β€” I'm as torn as you are there!

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Oh, yes! Totally β€” and thank you! I actually wanted to include this as well but had to run for a lecture. I'll include this wonderful example (I may just change the names so it's easier for tired folks to follow) in the blog tomorrow β€” look for the shoutout!

Collapse
 
yerlanyr profile image
yerlanyr

This thing I use a lot!

function foo(arg) {
  if (arg === "a") return 1
  if (arg === "b") return 2
  return 3 //default value
}
Enter fullscreen mode Exit fullscreen mode

At this point I always format if statements as if code block, because condition in if statement could be very long so that return would be lost dangling somewhere outside of field of view which could lead to bad mistakes.

function foo(arg) {
  if (arg % 3 === 0 && arg % 5 == 0 /* let's pretend there is very long condition*/) return 'foobar'
  if (arg % 3 === 0) return 'foo'
  if (arg % 5 === 0) return 'foo'
}
Enter fullscreen mode Exit fullscreen mode

Data structures are good for reducing code's complexity. Sometimes it is clearer to use switch case or if's.

Collapse
 
sylwiavargas profile image
Sylwia Vargas

I love these examples β€” thank you!

condition in if statement could be very long so that return would be lost dangling somewhere outside of field of view
I really couldn't agree more. This is definitely one of the main things that bother me about JS specifically β€” that there's no strict standard/expectation of writing really short code.

Collapse
 
aminnairi profile image
Amin • Edited

Hi there, great article, thank you!

I like to deal with all the error cases first, and then dealing with the heart of the function. Also I like to create small functions that deal with a single responsibility, this is easier to work with IMO.

I have sort of a kink with promises now and I like to put them everywhere. I like the simplicity of chaining functions.

"use strict";

const string = something => JSON.stringify(something);

const divide = (numerator, denominator) => new Promise((resolve, reject) => {
    if (typeof numerator !== "number") {
        return reject(new TypeError(`numerator should be a number in divide(${string(numerator)}, ${string(denominator)})`));
    }

    if (typeof denominator !== "number") {
        return reject(new TypeError(`denominator should be a number in divide(${string(numerator)}, ${string(denominator)})`));
    }

    if (0 === denominator) {
        return reject(new Error(`denominator should not be zero in divide(${string(numerator)}, ${string(denominator)})`));
    }

    return resolve(numerator / denominator);
});

divide(1, 2)
    .then(result => divide(result, 2))
    .then(result => divide(result, 2))
    .then(result => console.log(`After dividing by two three times: ${result}.`))
    // After dividing by two three times: 0.125.
    .catch(({message}) => console.error(`error while dividing: ${message}.`));

divide(1, 0)
    .then(result => divide(result, 2))
    .then(result => divide(result, 2))
    .then(result => console.log(`After dividing by two three times: ${result}.`))
    .catch(({message}) => console.error(`error while dividing: ${message}.`));
    // error while dividing: denominator should not be zero in divide(1, 0).
Enter fullscreen mode Exit fullscreen mode
Collapse
 
rasmusvhansen profile image
rasmusvhansen

I am not sure turning inherently synchronous code into async is a good idea. Promises are OK (not great - observables are better in many cases) for async operations but I would definitely avoid introducing the complexity for inherently sync operations.

By using this pattern, you are forcing all your code to be async.

Collapse
 
eecolor profile image
EECOLOR

If you use async your code becomes a bit more natural:

async function divide(numerator, denominator) {
    if (typeof numerator !== "number") {
        throw new TypeError(`numerator should be a number in divide(${numerator}, ${denominator})`);
    }

    if (typeof denominator !== "number") {
        throw new TypeError(`denominator should be a number in divide(${numerator}, ${denominator})`);
    }

    if (0 === denominator) {
        throw new Error(`denominator should not be zero in divide(${numerator}, ${denominator})`);
    }

    return numerator / denominator;
});
Enter fullscreen mode Exit fullscreen mode

This however indicates that it would be probably be smart to remove the async and move that to a separate function. That would allow you to use the divide function in more scenario's.

Collapse
 
sylwiavargas profile image
Sylwia Vargas

THANK YOU! YES, I was soooo tempted to touch on Promises but then majority of folks who read my blogs (maybe less so now?) are beginners so I'm planning to write a separate thing on promises in general. However, I'll link your comment in the article because I love your example! Thank you.

Collapse
 
dhintz89 profile image
Daniel Hintz

This is an awesome demonstration! I need to start learning and living this pattern for larger functionality.

Collapse
 
merri profile image
Vesa Piittinen

Tip: instead of something === undefined && something === null you can write something == null and it matches both undefined and null, and only them.

I find it the only valid case to use == over ===.

Collapse
 
drarig29 profile image
Corentin Girard

That's true, but oftentimes you have a linter which forces to use "eqeqeq"

Collapse
 
merri profile image
Vesa Piittinen

Only if you have had someone strongly opinioned setting it up :) And even then you have the null: ignore option for it.

Collapse
 
sylwiavargas profile image
Sylwia Vargas

True! Thanks!

Collapse
 
bjornet profile image
BjΓΆrn Christensson

Tnx for this list.

Minor feedback in the ✨ guard clauses

guardClauseFun("h") // => undefined with a warning
Enter fullscreen mode Exit fullscreen mode

It will not return undefined since you do not break the function flow, it will continue to the end and return "" (empty string).

Collapse
 
vidhill profile image
David Hill • Edited

yup,
a solution would be to add a return before the console.warn then it would return undefined

if (str.length <= 3) return console.warn("your string should be at least 3 characters long and its length is", str.length) 
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sylwiavargas profile image
Sylwia Vargas

Ah! True. I edited that part and didn't edit the examples. Argh I should write unit tests for my blogs 😩 Thank you!

Collapse
 
bjornet profile image
BjΓΆrn Christensson

That is the way to go! Smart, if all code samples came from actual unit tests eg. Mocha you would also practice the mentality of "placing tests in the first room".

Thread Thread
 
sylwiavargas profile image
Sylwia Vargas

Yeah I might try it in some future blogs. I've always been a fan of TDD but never made space to properly go through all the phases and the process because I felt there was "not enough time". I'm slowly changing this mindset not only because I feel like TDD is really awesome but also because of how the "not enough time" mindset impacts me and my ability to code at times.

Collapse
 
vidhill profile image
David Hill

One thing I see on occasion,

is the resulting action being calling a function, with the only difference being some logic determining what a certain argument should be

const doSomething = function (arg1, arg2) {
  if (arg1 === "condition") {
    return callA(arg1, arg2, 10);
  }
  return callA(arg1, arg2, 0);
};
Enter fullscreen mode Exit fullscreen mode

versus

const doSomethingB = function (arg1, arg2) {
  const arg3 = arg1 === "condition" ? 10 : 0;
  return callA(arg1, arg2, arg3);
};
Enter fullscreen mode Exit fullscreen mode

Another one is calling functions with the same arguments, with the only difference being which function to call:

const doSomething = function (arg1, arg2, arg3) {
  if (arg1 === "condition") {
    return callA(arg1, arg2, arg3);
  }
  return callB(arg1, arg2, arg3);
};
Enter fullscreen mode Exit fullscreen mode

Versus

const doSomething = function (arg1, arg2, arg3) {
  const fnToCall = arg1 === "condition" ? callA : callB;
  return fnToCall(arg1, arg2, arg3);
};
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sylwiavargas profile image
Sylwia Vargas

Thank you for these examples! Coming from Ruby, this is something I definitely instinctively lean towards and catch myself writing sometimes πŸ˜‚ I'll include you're examples in the blog post!

Collapse
 
cknott profile image
cknott

I think theres a typo in the last example of the 2nd block "OR operator"

this

  let sumFunctionWithOr = (a, b, inconsistentParameter) => {
    inconsistentParameter = inconsistentParameter ?? 0
    return a+b+inconsistentParameter
}
Enter fullscreen mode Exit fullscreen mode

should be

  let sumFunctionWithOr = (a, b, inconsistentParameter) => {
    inconsistentParameter = inconsistentParameter || 0
    return a+b+inconsistentParameter
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sylwiavargas profile image
Sylwia Vargas

Ahhhh thank you! That's what happens when you copy examples mindlessly 😩

Collapse
 
thexdev profile image
M. Akbar Nugroho

It's very awesome when you use guard clause to handle multiple condition instead of using if elseif else statement.

I'm a big fan of it and always use it to handle conditional statement in my code :).

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Ahhhh I'm also such a fan of guard clauses! My first coding language is and was Ruby, which is obsessed with readable and pleasant code so of course, the looong code monsters that JS awakens from the deepest depth of programming hell gave me chills initially. I feel like my brain fries when I read nested if-elses... there should be an ESLint rule that obliges devs to draw a flowchart every time they write a nested if-else so it's quick and easy to follow :D

Collapse
 
mcsee profile image
Maxi Contieri

Nice!

This is applied to structured programming and these operators are great.

In OOP you can remove all accidental IFs and elses

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Awesome! I've linked up your blog post in mine just now!

Collapse
 
mtancoigne profile image
Manuel Tancoigne • Edited

I mainly develop in Ruby and that makes me love guard clauses. Even our linter enforces us to use them for the sake of readability, and it looks awesome :)

raise 'This is not possible' if impossible?

# code continues if not impossible?
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sylwiavargas profile image
Sylwia Vargas

Ruby πŸ₯° Guard clauses πŸ₯° Ruby Linters πŸ₯°

Collapse
 
kiddyxyz profile image
Muhamad Hudya Ramadhana

If you have more than one condition, why you just not using an array rather than or?

let arr = [null, undefined, '']
if (x in arr) {
   // code
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sylwiavargas profile image
Sylwia Vargas

Yeah it's one way to do it but that still keeps the same if-else (or just no-return-statement) logic that we want to ideally get rid of. Here I'd also worry about the performance as if-else is costly and so is looping and here we'd have looping inside if-else. But I like this example β€” thank you!

Collapse
 
abelardoit profile image
abelardoit • Edited

Hi there,

I would opt to reject any non-numeric value to compute any calculus.

If you provide a non-number to compute a sum, then the precondition is not valid; therefore, my function would throw an exception.

Nice article! Thanks for bring it us! Best regards.

Collapse
 
afpaiva profile image
Andre Paiva

Hi Sylwia. Great article, congrats!

Let me do some noob questions?
Using [switch] in a situation with many [if/else if], will offer a better performance?
And is there difference by using [switch] or [if] or vice versa on a compiled or non compiled programming language? Like, on C it would be better this, and on JS better that?

Thanks a lot!

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Hi @afpaiva ! Thank you for your question!
In comparison with if/else statements, switch statements are a bit faster with small number of cases and get incrementally faster with new conditions. Readability, it seems that devs prefer to read if/else for two conditions and then switches for more.
There's this great table from O'reilly:
performance table comparing switches, if/else and table lookups

Talking about performance in C is both beyond my expertise and comfort level, sadly!

Collapse
 
anu1411 profile image
anu1411 • Edited

Hi my code is like below, can u suggest how can I refactor this:

`if (Object.prototype.hasOwnProperty.call(schema.properties, key)) {
                var prop = schema.properties[key];
                if (object[key]) continue

               else if (prop.type === 'string' && !prop.enum) {
                object[key] = "";
                continue;
                }
               else if (prop.type === 'relationship') {
                object[key] = null; 
                continue;
                }
                else if (prop.type === 'array') {
                    object[key] = [];
                    continue;
                }
                else if (prop.type === 'object') {
                    object[key] = {};
                    continue;
                }
            }`
`


Enter fullscreen mode Exit fullscreen mode
Collapse
 
dankimhaejun profile image
Dankimhaejun • Edited

let nestedIfElseHell = (str) => {
if (typeof str == "string"){
if (str.length > 1) {
return str.slice(0,-1)
} else {
return null
}
} else {
return null
}
}


why don't you use like this?

let nestedIfElseHell = (str) => {
if (typeof str === "string && str.length >1) {
return str.slice(0,-1);
}

return null;
}

or
let nestedIfElseHell = (str) => {
if (isStringAndHasLength(str)) {
return str.slice(0,-1)
}

return null;
}

let isStringAndHasLength = (str) => typeof str === "string" && str.length > 1

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Definitely! I like that you are using the typical for OOP callbacks to do the if/else job! Thanks!

Collapse
 
morgvanny profile image
Morgan VanYperen

oh hi! I didn't realize I knew who wrote the article until I got to the comments lol. good post!

Collapse
 
sylwiavargas profile image
Sylwia Vargas

hello! ✨ good to see you here! it's funny how the tech world is both big and small πŸ˜‚

Collapse
 
_hs_ profile image
HS

Since your shorting out the code I expected something like

let noElseReturns = (str) => {
  if (typeof str == "string" && str.length > 1) {
      return str.slice(0,-1)
  }
  return null
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
sylwiavargas profile image
Sylwia Vargas

yeah, that totally works too! Thanks for this comment!
I always try to balance how much I'm shortening the code vs how long the blog post is as my blogs posts are oftentimes read by folks with not much programming experience. Sometimes, I prefer to introduce changes incrementally or even not to introduce something because I also trust that the readers (just like yourself) would dig more or even find better solutions ✨

Collapse
 
marln94 profile image
marln94

I've been using guard clauses for a while but I didn't know they were called like that!
Great post πŸŽ‰

Collapse
 
sylwiavargas profile image
Sylwia Vargas

Thank you! Yeah they definitely ✨ spark joy ✨

Collapse
 
phongduong profile image
Phong Duong

JS has more useful features that make my life easier when writing conditions. Thank you

Collapse
 
peppermint_juli profile image
Juliana Jaime πŸŽƒ

I think after starting to use Typescript I haven't had most of these problems

Collapse
 
gene profile image
Gene

"Geeezz, skip all these and just use typescript."

:/

Collapse
 
detunized profile image
Dmitry Yakimenko

Oh my! Poor Javascript developers.

Collapse
 
chitreshgoyal profile image
Chitresh Goyal

Can you help me refactoring dev.to/chitreshgoyal/refactor-java... code