Why is no error thrown for infinite loops

user_16983447 0
Viewed 91

This is my code snippet

const loopFn = function(num) {

  for(let a = 0; a < num || 10; a++) { 
    console.log(a)
  }

}

let b = loopFn(8)

console.log(b)

I know the correct way to write is a < (num || 10), I'm just curious why it causes an infinite loop instead of reporting an error.

html javascript
6 Answers

What you mean do to is

const count = num || 10;

for(let a = 0; a < count; a++) { 
    console.log(a)
}

But what you're actually doing is saying while a is less than 8 OR 10 is true

user_5551480

The language/execution engine does not report it as an error because there is no inherent issue with infinite loops itself.

Depending upon the use-case infinite loops are of help. For instance, in daemon scripts that are meant to process jobs from a queue.

user_31537860

The condition of your for loop is:

a < num || 10

If either a < num is true, or 10 is true the loop continues.

Try in your browser console, and you will see, that 10 is always true. if(10) alert("true")

If you want the loop to end if a is not < 10, try this:

for(let a = 0; a < num || a < 10; a++)
user_153552280

The second part of for loop is condition; and boolean result of that condition tells the for loop to stop or continue; when you put 10 it will be evaluated as true; hence for loop never end; as if you writing

if (10) {
  // do something
}
user_59536100

If you are not wrapping the logic inside brackets, then it will divide like this

either it will check a<num is true or 10 is a true expression.

It taking 10 as a true expression because its a non zero number. So every time the loop getting the second expression as true and so on.

If you wrap the condition then it will check like this

either a<num or a<10

It will stop when it match any of the expression false.

It just the use of brackets.

user_117010320

The reason is because of the Operator Precedence in JavaScript (or any language). When you pass the expression a<num||10 to your for loop's break condition, it evaluates the a<num part first, and then the ||10 part. a<num will provide you with a true/false value and 10 will give you 10 (a truthy value), hence a<num||10 will essentially check if one of a<num or 10 is a truthy value, which is true. Therefore, the infinite loop.
More on Operator Precedence: MDN Docs

user_113042030
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