Damian Cipolat

Posted on Mar 2, 2020 • Edited on Mar 5, 2020

Avoid use IF on our JS scripts

#javascript #if #patterns

Well, I write this article because lately I was dealing with source code in js that had an excessive amount of if statement,
at levels that I had never seen. That is why I think it is very important to share these simple techniques that will help us to write code without having to think about the "if" when deciding.

I am going to explain 6 ways on how to do this. The idea of this is not to enter into paranoia of never using IF, it is to open the head to new ways of thinking about our decisions in JS.

1) Ternary operator:

We are talking about this "condition ? expr1 : expr2", very easy.

Example 1:

Code with IF:

function saveCustomer(customer) {
  if (isCustomerValid(customer)) {
    database.save(customer)
  } else {
    alert('customer is invalid')
  }
}

Refactored code:

function saveCustomer(customer) {
  return isCustomerValid(customer)
    ? database.save(customer)
    : alert('customer is invalid')
}

ES6 style:

const saveCustomer = customer =>isCustomerValid(customer)?database.save(customer):alert('customer is invalid')

Example 2:

Code with IF:

function customerValidation(customer) {
  if (!customer.email) {
    return error('email is require')
  } else if (!customer.login) {
    return error('login is required')
  } else if (!customer.name) {
    return error('name is required')
  } else {
    return customer
  }
}

Refactored code:

// ES6 style custom formatted ternary magic
const customerValidation = customer =>
  !customer.email   ? error('email is required')
  : !customer.login ? error('login is required')
  : !customer.name  ? error('name is required')
                    : customer

Example 3:

Code with IF:

function getEventTarget(evt) {
    if (!evt) {
        evt = window.event;
    }
    if (!evt) {
        return;
    }
    const target;
    if (evt.target) {
        target = evt.target;
    } else {
        target = evt.srcElement;
    }
    return target;
}

Refactored code:

function getEventTarget(evt) {
  evt = evt || window.event;
  return evt && (evt.target || evt.srcElement);
}

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2) Short circuit:

It is a technique that uses the AND and OR operators to evaluate expressions.

https://codeburst.io/javascript-short-circuit-conditionals-bbc13ac3e9eb

true || true;
// true
true || false;
// true
false || false;
// false

Example 1:

Code with IF:

const isOnline = true;
const makeReservation= ()=>{};
const user = {
    name:'Damian',
    age:32,
    dni:33295000
};

if (isOnline){
    makeReservation(user);
}

Refactored code:

const isOnline = true;
const makeReservation= ()=>{};
const user = {
    name:'Damian',
    age:32,
    dni:33295000
};

//Apply the short circuit to avoid the if.
isOnline&&makeReservation(user);

Example 2:

Code with IF:

const active = true;
const loan = {
    uuid:123456,
    ammount:10,
    requestedBy:'rick'
};

const sendMoney = ()=>{};

if (active&&loan){
    sendMoney();
}

Refactored code:


const active = true;
const loan = {
    uuid:123456,
    ammount:10,
    requestedBy:'rick'
};

const sendMoney = ()=>{};

//Apply short circuit in this case, the loan is evaluated true because !=undefined
active && loan && sendMoney();

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3) Function delegation:

This technique mix the short circuit and separation code block with functions.

Example 1:

Code with IF:

function itemDropped(item, location) {
    if (!item) {
        return false;
    } else if (outOfBounds(location) {
        var error = outOfBounds;
        server.notify(item, error);
        items.resetAll();
        return false;
    } else {
        animateCanvas();
        server.notify(item, location);
        return true;
    }
}

Refactored code:

function itemDropped(item, location) {
    const dropOut = function() {
        server.notify(item, outOfBounds);
        items.resetAll();
        return false;
    }

    const dropIn = function() {
        server.notify(item, location);
        animateCanvas();
        return true;
    }

    return !!item && (outOfBounds(location) ? dropOut() : dropIn());
}

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4) Non branching strategy:

This technique try to avoid the use of switch statemente. The idea is to create a map with keys/values and using a function
to access the value of the key passed as parameter.

The idea came from this link: https://medium.com/chrisburgin/rewriting-javascript-replacing-the-switch-statement-cfff707cf045

Example 1:

Code with SWITCH:

switch(breed){
    case 'border':
        return 'Border Collies are good boys and girls.';
        break;  
    case 'pitbull':
        return 'Pit Bulls are good boys and girls.';
        break;  
    case 'german':
        return 'German Shepherds are good boys and girls.';
        break;
    default:
        return 'Im default'

}

Refactored code:


const dogSwitch = (breed) =>({
  "border": "Border Collies are good boys and girls.",
  "pitbull": "Pit Bulls are good boys and girls.",
  "german": "German Shepherds are good boys and girls.",  
})[breed]||'Im the default';


dogSwitch("border xxx")

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5) Functions as Data:

We know that in JS the function are first class, so using it we can split the code into a function objects.

Example 1:

Code with IF:


const calc = {
    run: function(op, n1, n2) {
        const result;
        if (op == "add") {
            result = n1 + n2;
        } else if (op == "sub" ) {
            result = n1 - n2;
        } else if (op == "mult" ) {
            result = n1 * n2;
        } else if (op == "div" ) {
            result = n1 / n2;
        }
        return result;
    }
}

calc.run("sub", 5, 3); //2

Refactored code:

const calc = {
    add : function(a,b) {
        return a + b;
    },
    sub : function(a,b) {
        return a - b;
    },
    mult : function(a,b) {
        return a * b;
    },
    div : function(a,b) {
        return a / b;
    },
    run: function(fn, a, b) {
        return fn && fn(a,b);
    }
}

calc.run(calc.mult, 7, 4); //28

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5) Polymorphism:

Polymorphism is the ability of an object to take on many forms. The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object.

Example 1:

Code with IF:

const bob = {
  name:'Bob',
  salary:1000,
  job_type:'DEVELOPER'
};

const mary = {
  name:'Mary',
  salary:1000,
  job_type:'QA'
};

const calc = (person) =>{

    if (people.job_type==='DEVELOPER')
        return person.salary+9000*0.10;

    if (people.job_type==='QA')
        return person.salary+1000*0.60;
}

console.log('Salary',calc(bob));
console.log('Salary',calc(mary));

Refactored code:

//Create function to different behaviour, same parameter call.
const qaSalary  = (base) => base+9000*0.10;
const devSalary = (base) => base+1000*0.60;

//Add function to the object.
const bob = {
  name:'Bob',
  salary:1000,
  job_type:'DEVELOPER',
  calc: devSalary
};

const mary = {
  name:'Mary',
  salary:1000,
  job_type:'QA',
  calc: qaSalary
};

//Same call.
console.log('Salary',bob.calc(bob.salary));
console.log('Salary',mary.calc(mary.salary));

⮬ back to top

Readings:

A list of interesting links about this same topic.

Visit my github for more projects!!
https://github.com/damiancipolat?tab=repositories

Top comments (47)

Tomer • Mar 2 '20

Nice article , but i always prefer readability over number of lines :)

Comment marked as low quality/non-constructive by the community. View Code of Conduct

Víctor Falcón • Mar 4 '20

True, and some example on this article are horrible, in my opinion.

That second ternary almost explode my brain.

Damian Cipolat • Mar 4 '20

well bad luck, thanks for your opinion. I consider more horrible a code like this:

export const removeProps = (source: Object, props: Array, keepReceivedProps: boolean = true) => {
return Object.keys(source).forEach(key => {
if (keepReceivedProps) {
if (!props.find(item => item == key)) delete source[key];
} else {
if (props.find(item => item == key)) delete source[key];
}
});
};

This code is from a project make maybe from JAVA developers that come to JS or for JS Jr developer. the if nesting I think is very bad. So for this reason I'm looking for alternatives to avoid write this type of code and publish material to try the developers in find new alternatives

Luca Muscat • Mar 6 '20

Slight correction, it's no longer a ternary if it contains more than 3 values on the right hand side (it becomes an n-ary operator ;) )

Damian Cipolat • Mar 7 '20

NICE thanks for the data

Carlos Moran • Mar 5 '20

And the lack of spacing, my eslint config would choke on the examples.

Damian Cipolat • Mar 5 '20

They were not developed using eslint, you can execute them directly from node in a new project

Ben Calder • Mar 2 '20

Some useful suggestions here; but some should come with health warnings:

even a single nested ternary can be hard to read. Your example with multiple nesting should never get through code review. Nesting ternaries should be discouraged
short circuit can be useful; but can often result in mistakes: e.g. returning false when another type is expected (this is a good use for ternary). Linting rules often disallow conditionIsTrue && functionCall() outside an assignment expression.
the itemDropped example would work better using guard expressions: you still use if but can get rid of the redundant use of else. Simpler and more readable than your suggestion.

Damian Cipolat • Mar 2 '20

I am glad to see that it generates reactions in other devs, it is the idea of the article. As I said above, the idea is not to stop using if it's just something to shake them and they can think about decisions in another way.

Ben Calder • Mar 2 '20

Generating reactions is all well and good, but I think it would be more productive to put forward examples of alternatives to if in contexts where they are appropriate/useful. Given the introduction describing code with too many ifs; some junior devs may mistakenly believe all your solutions represent good practice...

Damian Cipolat • Mar 2 '20

In the header it says that they are clearly techniques and you should not go into paranoia. Maybe in future articles I will raise 'real' situations I am collecting many situations with many sentences of my work, but at the moment I do not have enough time to do something at that level.

Ivan • Mar 4 '20

The nested ternary hurts my brain, despite that, the article has a lot of gems, thanks guys!

Damian Cipolat • Mar 4 '20

hahaha yes is hard to process I know, but are just examples, the idea is to open the brain to new alternatives some very nice other heavy to understand.

JJankowski • Mar 25 '20

I totally agree that nested ternaries are a pain to read.

Also, the itemDropped sample looks very "magical" to a person not familiar with such paradigm.

Damian Cipolat • Mar 27 '20

Well the idea is to provide reason to star going deeper in JS.

Matthias Müller • Mar 2 '20

While you've shown some nice alternatives for IF, most of these examples feel less readable after being refactored. Especially chaining the ternary operator should be avoided IMHO.

Damian Cipolat • Mar 2 '20

Yes in the refactor, some of semantic is lost. The chaining ternaries is the most extreme. Consider this things as example you can chose use it or not.

diek • Mar 2 '20

Well well, i think we should program in human language, you are not doing it with this examples xD

Damian Cipolat • Mar 2 '20

Is the problem with the functional paradigm, is less semantic in comparation with oop.

kalium.xyz • Mar 2 '20

You can do functional fine with a more verbose language (e.g. rust allows for assignment with the result of an if statement), this is just a design choice of the language.

Having a more verbose language is not inherently bad nor are if statements not part of a proper functional language.

Matei Adriel • Mar 2 '20

Yep, most fp langs consider if statements simple expressions, so you can pass the results around

Michel Renaud • Mar 2 '20

I've had to deal with "overdone" uses of the ternary operator. I was not pleased.

Damian Cipolat • Mar 2 '20

The point of replacing the elseif with ternary nesting is hard to read. Another way could be to use a single level of if. but the idea of the article was to program without using a single if. I am open to see other devs as they would raise this.

Malte Büchmann • Mar 5 '20

Very nice article. But I think I found one catch:

The rewrite in the second example for ternary operators makes the code very unreadable. The cumbersome part of this example are the else statements. If you use guard clauses if statements, the code becomes much more readable and concise:

function customerValidation(customer) {
  if (!customer.email) {
    return error('email is require');
  } 
  if (!customer.login) {
    return error('login is required');
  }
  if (!customer.name) {
    return error('name is required');
  }
  return customer;
}

In this case, you can even remove the curly braces:

function customerValidation(customer) {
  if (!customer.email)
    return error('email is require');  
  if (!customer.login)
    return error('login is required');
  if (!customer.name)
    return error('name is required');

  return customer;
}

Now both versions are much more readable and the reader can understand the intent of the written code much better: catch errors and return them.

Damian Cipolat • Mar 5 '20

thanks for comment!

Raul • Mar 4 '20 • Edited

The article is nice, it gives some cool alternatives that not everyone might know about, a handful of which we use at work.

As others said, tho, some are harder to read.

A little side note about #4 and #5: it would be better to re-use the object and not to create it every time a function is called (eg: creating it inside array.map(), etc), it slows down your code a lot!

I'm saying this because it might not be obvious and also because I've had to refactor some code that was doing the exact same thing after I got hired 😊

A better approach would be to do something like this instead:

const createDogSwitcher = () =>{
  const objectSwitch = {
    border: 'Border Collies are good boys and girls.',
    pitbull: 'Pit Bulls are good boys and girls.',
    german: 'German Shepherds are good boys and girls.',  
  }

  const defaultString = 'Im the default.'

  return (breed) => objectSwitch[breed] || defaultString
}

const dogSwitch = createDogSwitcher()

dogSwitch('border xxx')

// Now use `dogSwitch` inside `map()`

If you want even better performance out of this, you can use a Map() instead of an object 🖖🏼

Edit: I think you have two #5s 🤔

Damian Cipolat • Mar 4 '20

thanks for comments! the idea was make an arrow function that return an object. I had thought about this option too, it is more semantic but much more code. It is in each developer as you feel more comfortable.

ezgif.com • Mar 3 '20 • Edited

TBH I think all of your examples are more readable with ifs, especially the nested ternaries. I would hate to see that in code I have to work with.

Ifs are very easy to read and understand, there is no performance problems with them. What do you gain from avoiding ifs?

William Kuang • Mar 2 '20 • Edited

No way is nested ternaries easier to read than if/else if statements. Teraries should be used for if/else statements only. Nesting them is insane. It reminds me of if/else if operations in Excel.

Damian Cipolat • Mar 2 '20

Yes is similar, the Excel formulas are something like fp

Sean O'Grady • Mar 5 '20

what do you mean by this?

William Kuang • Mar 19 '20

If you've ever had to write a conditional in Microsoft Excel, you'll be familiar with this. Check out this article to see what I mean: exceljet.net/excel-functions/excel....

Excel doesn't have if/else if statements, it only has if/else which is the same as a ternary. Do you really think reading this is easier?
=IF(C6<70,"F",IF(C6<75,"D",IF(C6<85,"C",IF(C6<95,"B","A"))))

Damian Cipolat • Mar 19 '20

It is just a proposal, for me an excel formula is just as ugly as an if..else..elseif with nesting.

Wilfredo Pérez • Mar 5 '20

Hey Damian the last example is not working.

//Create function to different behaviour, same parameter call.
const qaSalary  = (base) => base+9000*0.10;
const devSalary = (base) => base+1000*0.60;

//Add function to the object.
const bob = {
  name:'Bob',
  salary:1000,
  job_type:'DEVELOPER',
  calc: devSalary
};

const mary = {
  name:'Mary',
  salary:1000,
  job_type:'QA',
  calc: qaSalary
};

//Same call.
console.log('Salary',bob.calc());
console.log('Salary',mary.calc());

the output is:

Salary NaN
Salary NaN

Damian Cipolat • Mar 5 '20

:o :O yes that true, I will fix it. thanks for tell me.

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DEV Community

Avoid use IF on our JS scripts

Categories:

1) Ternary operator:

Example 1:

Example 2:

Example 3:

2) Short circuit:

Example 1:

Example 2:

3) Function delegation:

Example 1:

4) Non branching strategy:

Example 1:

5) Functions as Data:

Example 1:

5) Polymorphism:

Example 1:

Readings:

Top comments (47)

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