Using the switch(true) pattern in JavaScript

Re:Using the switch(true) pattern in JavaScript by tpoacher on Monday April 12, 2021 @03:41PM (#26784162)

I agree, but also I think this is misrepresenting the 'early return' pattern. It's more likely to be succinct and look like this instead:

    function check(x) {
        if (!test1 (x))   return false;
        if (!test2 (x))   return false;
        if (!test3 (x))   return false;
        if (!test4 (x))   return false;
        return true;
    }

In _this_ scenario, it is true that this is much more readable than:

    function check(x) {
        if (!test1 (x)) {
           return false; 
        } else if (!test2 (x)) {
           return false;
        } else if (!test3 (x)) {
           return false;
        } else if (!test4 (x)) {
           return false;
        } else {
           return true;
        }
    }

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Re:Using the switch(true) pattern in JavaScript by tsimionescu on Monday April 12, 2021 @03:51PM (#26784272)

Never ever use if without curly braces. That's one of the worst ideas of C's syntax.

Your first example would still look clean like this:

  function check(x) {
      if (!test1 (x)) { return false; }
      if (!test2 (x)) { return false; }
      if (!test3 (x)) { return false; }
      if (!test4 (x)) { return false; }
      return true;
  }

And it would be much safer from stupid copy/paste errors.

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Re:Using the switch(true) pattern in JavaScript by jhgb on Monday April 12, 2021 @05:53PM (#26785659)

Instead of

    function check(x) {
        if (!test1 (x))   return false;
        if (!test2 (x))   return false;
        if (!test3 (x))   return false;
        if (!test4 (x))   return false;
        return true;
    }

why wouldn't you do something along the lines of

    (every (lambda (f) (funcall f x)) (list #'test1 #'test2 #'test3 #'test4a))

or whatever is the equivalent in your preferred language?

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Re:Using the switch(true) pattern in JavaScript by wvenable on Monday April 12, 2021 @06:03PM (#26785743)

The tests are rarely that simple or regular.

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Re:Using the switch(true) pattern in JavaScript by jhgb on Monday April 12, 2021 @06:25PM (#26785943)

Isn't that exactly the reason to put them somewhere else?

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Re:Using the switch(true) pattern in JavaScript by wvenable on Monday April 12, 2021 @06:30PM (#26785995)

No, I just mean the actual tests might be something like:

    if (user == null) return false;
    if (IsCompleted(user)) return true;
    if (action == null) return false;
    if (value < 0 || value > 100) return false;

You're not usually just passing a single value to a bunch of "test" functions.

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Re:Using the switch(true) pattern in JavaScript by jhgb on Monday April 12, 2021 @08:18PM (#26786740)

Well, the way it was written, I was assuming that conditions to be satisfied had separate named predicates (although combinators could alleviate even some of these things).

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Re:Using the switch(true) pattern in JavaScript by brundolf on Monday April 12, 2021 @03:44PM (#26784191)

Worth noting that elses don't require curly braces, which are where most of the visual noise is coming from in your example:

  function check(x) {
    if (!test1 (x))      return false; 
    else if (!test2 (x)) return false;
    else if (!test3 (x)) return false;
    else if (!test4 (x)) return false;
    else                 return true;
  }

I think this is more clear than either of the above

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Re:Using the switch(true) pattern in JavaScript by tpoacher on Monday April 12, 2021 @03:49PM (#26784249)

> Worth noting that elses don't require curly braces

True. I still think the first is clearer though. Either all tests pass, or they don't.

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Re:Using the switch(true) pattern in JavaScript by tpoacher on Monday April 12, 2021 @03:50PM (#26784257)

(also I'd be very skeptical of such an if..else ladder. Prime target for bugs.)

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Re:Using the switch(true) pattern in JavaScript by alerighi on Monday April 12, 2021 @07:10PM (#26786293)

That code is ugly anyway, something I would have wrote in middle school... why not:

    function check(x) {
        return test1(x) && test2(x) && test3(x) && test4(x);
    }

Or, since I assume is JavaScript, just:

    const check = x => test1(x) && test2(x) && test3(x) && test4(x);

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Re:Using the switch(true) pattern in JavaScript by brundolf on Tuesday April 13, 2021 @12:29PM (#26794862)

Nobody would actually write this, it's just a demonstration of the pattern at hand for the sake of discussion

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