Why is the while condition not an infinite loop?

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Why the condition of this while is not a loop infinite?

function fibonacci(n) {


const fibSequence = [1];

let currentValue = 1;
let previousValue = 0;

if (n === 1) {
  return fibSequence;
}

let iterationsCounter = n - 1;

while (iterationsCounter) {
  currentValue += previousValue;
  previousValue = currentValue - previousValue;

  fibSequence.push(currentValue);

  iterationsCounter -= 1;
}

return fibSequence;
}
javascript comparison boolean

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1 answer

1

Javascript is a weak and dynamic typing language. This means that it makes value coercion whenever it is necessary to give a valid result.

That’s what gives the language a bad name, if it didn’t have the weak JS typing would be a language much closer to being very good. It gives an unnecessary facility for the person to learn the basics and use in a way apparently a little easier, but soon after you start doing more complex things it shows a huge problem, which becomes a joke at various times between developers. But look, this wasn’t supposed to be a problem, the language was created to make something very simple and give a little animation or do a simple action on a very simple web page. The problem was that they started making complex code on a single page which is a true application. The language is not suitable for this.

So whenever a site requires a boolean value of false or true, which is the case of a if or a while, the ideal is to generate a boolean value. But within the philosophy of weak typing JS, it makes any value a Boolean in some way, that is, it uses some rule of its own to convert another value, for example a number, into a Boolean. And it all works.

In that case there is a value in iterationsCounter which is considered a value Truthy, that is, it is true, because very few values are considered false. When this variable reaches a value Falsy the while turns fake and ends.

False values, according to the link above, are: false, 0, -0, 0n, null, undefined, NaN. So when the variable reaches the value 0 the condition is false. would be the same as saying more explicitly: iterationsCounter != 0.

The fact that bad choices have been made helps to give some problems, but not in this case. I wouldn’t even say that this shape is much less readable or cause so much confusion. Cause any.

That code has at least one bug. If the value is 0 or negative it does not work:

function fibonacci(n) {
    const fibSequence = [1];
    let currentValue = 1;
    let previousValue = 0;
    if (n === 1) return fibSequence;
    let iterationsCounter = n - 1;
    while (iterationsCounter) {
      currentValue += previousValue;
      previousValue = currentValue - previousValue;
      fibSequence.push(currentValue);
      iterationsCounter -= 1;
    }
    return fibSequence;
}

fibonacci(0);

I put in the Github for future reference.

It would be good to test this before reaching the loop and deciding what to do, probably not even returning a valid result.

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