Function property example explanation

Question

I was going through a JS tutorial, and came across this example:

function makeCounter() {
  function counter() {
    return counter.count++;
  };
  counter.count = 0;

  return counter;
}

let counter = makeCounter();
counter.count = 10;
console.log(counter()) // logs 10

What I don't understand is why it didn't log 11 instead of 10? If we have set the count property to 10 and stored the function counter that increments count property, why the property is not incremented then to 11?

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Increment_() — Andreas, Nov 17 '17 at 14:02
`counter()` will log `10`, but `counter.count` will log `11`. The `++` increment happens after the value is returned. If you want it before, you could write `return ++counter.count`. — skyline3000, Nov 17 '17 at 14:04

Hugo Migneron · Accepted Answer · 2018-02-07T20:11:24.680

3

You understand the function property well. This has to do with how ++ works.

return counter.count++; will return counter.count at its current value, THEN increment it, not the other way around.

edited Feb 07 '18 at 20:11

answered Nov 17 '17 at 14:01

Hugo Migneron

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Thank you very much, had no idea it was something that simple. – Leff Nov 17 '17 at 14:03

score 0 · Answer 2 · answered Nov 17 '17 at 14:03

0

Cause you are using the postfix increase operator, which firstly returns its current value, then it increases it. You could change that to a prefix increase:

   return ++counter.count;

answered Nov 17 '17 at 14:03

Jonas Wilms

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score -1 · Answer 3 · answered Nov 17 '17 at 14:03

-1

Your function makeCounter is returning a function, which has access to the [[scope]] . It's using closure. so It is obvious it works like that.

Closure : ' When a function memorizes the data from the place where he was called from' .

Further information ; What is a 'Closure'?

answered Nov 17 '17 at 14:03

Atlas

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I am thinking you missed the actual question. – epascarello Nov 17 '17 at 14:05

Function property example explanation

3 Answers3