✔||🤢 Commit or Vomit | Switch(true)

This could easily have been an if/elseif/else.

You could have done:

if(someExpressionA) console.log('yes')
else if ((someExpressionB 
    && someExpressionC) || someExpressionD) console.log('nope');
else console.log('maybe');

Since you're returning on each case I wouldn't even bother with elses...

if (useMissedAppointment) {
  return 'nope
}
if (userHasAngularExperience || useHasReactExperience || (userHasVieExperience && userCanStartImmediately)) {
  return 'hire'
}
return 'maybe'

Of course I'd also extract that second conditon into another method, but that's another matter.

I think the cleanest and most expressive is still this

const hasFrontendFrameworkExperience = userHasAngularExperience || userHasReactExperience || userHasVueExperience;

if(userMissedAppointment){
    return 'nope';
} else if(hasFrontendFrameworkExperience && userCanStartInstantly){
    return 'hire';
}
return 'maybe';

Why the need for the case statement?

if (userMissedAppointment) {
  return 'nope';
}
const userMeetsTechRequirements = userHasAngularExperience || userHasReactExperience || userHasVueExperience;
if (userMeetsTechRequirements && userCanStartInstantly) {
   return 'hire';
}
return 'maybe'

Also, imo, there's no need to repeat "user" in these flags. You could just say canStartInstantly, for example. There's no ambiguity regarding who this refers to.

While the code is valid, I think the real issue here is just the amount of conditions you're trying to parse through. Using switch (true) feels more like a band-aid than a solution I would accept say in a PR.

I'm a fan for using switches when we're actually comparing the value in switch(value). Someone mentioned checking for a match in the zodiac. Perfect use case for a switch statement.

When you have to resort to a hacky solution, chances are the problem lies more with the code leading up to this decision than the decision itself.

I think this is a misuse of the switch statement and its purpose.

If there is a need for this kind of hackery witchery I believe there are other design flaws which makes this code "necessary" and should be refactored to make this kind of code avoidable.

When an if statement gets so complex that you start to search for more readable ways of writing it there will most likely also be alternative ways to take it apart into smaller parts and make it more comprehensible (and maintainable) that way.

I'd say probably vomit, but I'm sure there are cases where this way is just easier to read than if/else/return early/etc. Hard to say with placeholder-var-names.

Honestly you made me really curious about the performance... The switch normally are the first choice to avoid writing long if-else chains because the code "jumps" directly to the right place without evaluating all the other conditions... I'm curious to understand if also in this case these considerations are valid or not... I'll try and, if so, it will be an heart

What do you think about switch(true) in general?

👎

With that out of the way I do think it's worth hypothesising how code like this may have come in to being.

But even before that I'm surprised nobody claimed primitive obsession given that there are five distinct boolean values on the "loose".

Seems the more likely scenario should be something like:

const results = {
  noShow: false,
  immediateAvailability: true,
  experience: {
    angular: false,
    react: false,
    vue: true,
  },
};

With that reorganization my next guess should make more sense. I suspect the switch(true) is a degenerate form of some copy-pasted code that was trying to approximate pattern matching.

While a number of languages support pattern matching, JavaScript only supports destructuring assignment — not pattern matching:

The big difference is simple: Pattern matching is a conditional construct and destructuring isn’t.

There is a TC 39 proposal to add pattern matching to JavaScript (which hasn't moved beyond stage 1 since 2018). Meanwhile there are some third party libraries available that approximate some pattern matching functionality.

Using Pattern Matching:

import { when, _ } from 'pattern-matching-js';
// https://github.com/klo112358/pattern-matching-js

const STATUS = {
  reject: 'nope',
  accept: 'hire',
  reevaluate: 'maybe'
};

const results = {
  noShow: true,
  immediateAvailability: true,
  experience: {
    angular: false,
    react: true,
    vue: false
  }
};

/* eslint-disable no-unexpected-multiline */
// prettier-ignore
const status = when(results)
  ({ noShow: true }, STATUS.reject)
  ({ experience: { angular: true } }, STATUS.accept)
  ({ experience: { react: true } }, STATUS.accept)
  ({ experience: { vue: true },
     immediateAvailability: true }, STATUS.accept)
  (_, STATUS.reevaluate)
  ();

console.log(status);

The actual proposal has much richer functionality that would allow for the aggregation of all the "accept" patterns. But if you squint, that when (or match) is reminiscent of a switch.

There is another way to represent boolean values - as bit flags.
Using bit flags/field operators:

const STATUS = {
  reject: 'nope',
  accept: 'hire',
  reevaluate: 'maybe',
};

const FLAGS = {
  noShow: 0x01,
  availableImmediately: 0x02,
  angular: 0x04,
  react: 0x08,
  vue: 0x10,
};

const results = FLAGS.availableImmediately | FLAGS.vue;
const status = interviewStatus(results);

console.log(status);

function interviewStatus(results) {
  if (match(results, FLAGS.noShow)) return STATUS.reject;

  if (
    match(results, FLAGS.angular) ||
    match(results, FLAGS.react) ||
    match(results, FLAGS.vue | FLAGS.availableImmediately)
  )
    return STATUS.accept;

  return STATUS.reevaluate;
}

function match(value, flags) {
  return (value & flags) === flags;
}

Again interviewStatus() is somewhat reminiscent of a switch statement wrangled to behave like an expression.

One final point: readability.

It's kind of interesting how many comments claim that if based solutions are more readable. Personally I find that most of the if based proposals require a prolonged mental parse to just get the gist of the code. Obviously readability is a lot more subjective than most people are willing to admit.

Using the nullish coalscing operator:

const STATUS = {
  reject: 'nope',
  accept: 'hire',
  reevaluate: 'maybe',
};

const results = {
  noShow: false,
  immediateAvailability: false,
  experience: {
    angular: false,
    react: false,
    vue: true,
  },
};

const status = interviewStatus(results);

console.log(status);

function interviewStatus(results) {
  return maybeReject(results) ?? maybeAccept(results) ?? STATUS.reevaluate;
}

// "maybe" prefix - returns a value or `undefiend`
function maybeReject({ noShow }) {
  return noShow ? STATUS.reject : undefined;
}

function maybeAccept({
  experience: { angular, react, vue },
  immediateAvailability,
}) {
  return angular || react || (vue && immediateAvailability)
    ? STATUS.accept
    : undefined;
}

In my view:

• the rejection criteria can be easily located and identified quickly
• the acceptance criteria can be easily located and identified fairly quickly
• it should be obvious that rejection criteria take precedence over acceptance criteria

Now I'm certain there already is a queue of people forming getting ready to drop a ton of bricks on me, how they don't find the above code readable at all.

That's not surprising — something is only judged as "readable" if it is already familiar. Anything unfamilar to an individual is also not as readable because of the additional cognitive effort that is required to read it.

In natural langauge there is the notion that

If you learn only 800 of the most frequently-used lemmas in English, you'll be able to understand 75% of the language as it is spoken in normal life.

However

Eight hundred lemmas will help you speak a language in a day-to-day setting, but to understand dialogue in film or TV you'll need to know the 3,000 most common lemmas.

Going further

And if you want to get your head around the written word - so novels, newspapers, excellently-written … articles - you need to learn 8,000 to 9,000 lemmas.

So just because something isn't deemed "readable" by a certain group of people doesn't necessarily imply that it is unreasonable.

From that point of view it's important to get exposure to a broad spectrum of programming styles (preferably across languages from different programming paradigms) — with that exposure a lot more code becomes "readable".

I can't believe some people put hearts

Vomit.
Either a verbose aggregation of desired Boolean checks OR return from currying some composable functions that return a similar aggregation.
I am slightly partial to the second as I believe anyone looking for FP would be.

How about that (pre-enterprise example :))

//allocate in one place binding of all rules with results
const conditionsEnum = {
  nope: ignoringConditions,
  hire: hiringConditions,
  maybe: mbConditions,
}

let result = '';

//find first truth in there
for (let field in conditionsEnum) {
  if (conditionsEnum[field].some(condition => !!condition())) {
    result = field;

    return result;
  }
}

values in object are just arrays of functions:

const ignoringConditions = [
  () => false,
  () => false,
  () => false,
]

const hiringConditions = [
  () => true,
  () => false,
  () => false,
]

const mbConditions = [
  () => false,
  () => false,
  () => false,
]

Hope my nickname speaks for itself

This was a tough one for me, I like the style, but if/else is easier to read and comprehend. so for me it's a 🤢

This code definitely smells. So you have multiple conditions that are all mutually exclusive, but not similar enough that you can't just use a regular switch?

In any case, that's not what switch is for. If-else that stuff. Or, even better in this case, just if's because return ends control flow anyways.

You can always (and probably should) refactor long bool expressions into a functions with descriptive names.