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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...

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bugb • Nov 17 '20

Suppose you have a code like this:

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

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;
}

Robert Myers • Nov 17 '20

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.

EECOLOR • Nov 19 '20

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
  )
}

or this:

function foo(arg) {
  return {
    a:  1,
    b:  2,
  }[arg] || 3
}

HS • Nov 17 '20 • 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.

rasmusvhansen • Nov 18 '20 • 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;

part.

HS • Nov 18 '20 • 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

rasmusvhansen • Nov 18 '20

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

xtofl • Dec 13 '20

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

João Ferreira • Nov 25 '20 • 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.

João Ferreira • Nov 25 '20

"too" was mistype, but let it be

Sylwia Vargas • Nov 17 '20

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 — I'm as torn as you are there!

Sylwia Vargas • Nov 17 '20

Oh, yes! Totally — 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 — look for the shoutout!

yerlanyr • Nov 21 '20

This thing I use a lot!

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

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'
}

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

Sylwia Vargas • Nov 21 '20

I love these examples — 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 — that there's no strict standard/expectation of writing really short code.

Amin • Nov 17 '20 • 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).

rasmusvhansen • Nov 18 '20

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.

EECOLOR • Nov 20 '20

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;
});

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.

Sylwia Vargas • Nov 17 '20

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.

Daniel Hintz • Nov 17 '20

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

Vesa Piittinen • Nov 17 '20

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 ===.

Corentin Girard • Nov 17 '20

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

Vesa Piittinen • Nov 18 '20

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

Sylwia Vargas • Nov 17 '20

True! Thanks!

Björn Christensson • Nov 17 '20

Tnx for this list.

Minor feedback in the ✨ guard clauses

guardClauseFun("h") // => undefined with a warning

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

David Hill • Nov 17 '20 • 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)

Sylwia Vargas • Nov 17 '20

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

Björn Christensson • Nov 17 '20

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".

Sylwia Vargas • Nov 17 '20

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.

David Hill • Nov 17 '20

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);
};

versus

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

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);
};

Versus

const doSomething = function (arg1, arg2, arg3) {
  const fnToCall = arg1 === "condition" ? callA : callB;
  return fnToCall(arg1, arg2, arg3);
};

Sylwia Vargas • Nov 17 '20

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

cknott • Nov 17 '20

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
}

should be

  let sumFunctionWithOr = (a, b, inconsistentParameter) => {
    inconsistentParameter = inconsistentParameter || 0
    return a+b+inconsistentParameter
}

Sylwia Vargas • Nov 17 '20

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

M. Akbar Nugroho • Nov 17 '20

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 :).

Sylwia Vargas • Nov 17 '20

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

Maxi Contieri • Nov 16 '20

Nice!

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

In OOP you can remove all accidental IFs and elses

How to Get Rid of Annoying IFs Forever

Maxi Contieri ・ Nov 9 ・ 5 min read

#oop #programming #codenewbie #tutorial

Sylwia Vargas • Nov 16 '20

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

Manuel Tancoigne • Nov 25 '20 • 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?

Sylwia Vargas • Nov 25 '20

Ruby 🥰 Guard clauses 🥰 Ruby Linters 🥰

Muhamad Hudya Ramadhana • Nov 17 '20

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
}

Sylwia Vargas • Nov 17 '20

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 — thank you!

abelardoit • Nov 17 '20 • 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.

Andre Paiva • Nov 17 '20

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!

Sylwia Vargas • Nov 21 '20

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:

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

anu1411 • Sep 14 '22 • 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;
                }
            }`
`

Dankimhaejun • Nov 17 '20 • 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

Sylwia Vargas • Nov 17 '20

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

Morgan VanYperen • Nov 19 '20

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

Sylwia Vargas • Nov 20 '20

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

HS • Nov 17 '20

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
}

Sylwia Vargas • Nov 17 '20

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 ✨