-- , -= 1 和 - 1 之间的区别

Question

I have been working through some freeCodeCamp exercises and while working on a recursion problem in which all the numbers between a given range have to be added to an array (including both the numbers), I came across a problem where the following works:

function rangeOfNumbers(startNum, endNum) {
  if (endNum - startNum === 0) {
    return [startNum];
  } else {
    let rangeArray = rangeOfNumbers(startNum, endNum - 1);
    rangeArray.push(endNum);
    return rangeArray;
  }
};

console.log(rangeOfNumbers(8 , 16));

but this doesn't:

function rangeOfNumbers(startNum, endNum) {
  if (endNum - startNum === 0) {
    return [startNum];
  } else {
    let rangeArray = rangeOfNumbers(startNum, endNum -= 1);
    rangeArray.push(endNum);
    return rangeArray;
  }
};

console.log(rangeOfNumbers(8 , 16));

There's no error but using the latter (-= 1), I am unable to reach the desired result (the resulting array excludes the upper limit of the range which is 16 in this case and instead includes one extra value of the lower range limit). Please explain how does the two work differently and the resulting effect in the code posted above. Thank You.

PS: I tried googling and even searched Stackoverflow. Coding is new to me and based on what I understood on MDN, 5 - 1 is pretty much the same as x -= 1 (where x = 5). Any help in terms of a different explanation is much appreciated.

Answer 1

The difference are:

--

i = 1
x = 1 + i-- // i = i - 1 after returning i
// i: 0, x: 2

i = 1
x = 1 + --i // i = i - 1 before returning i
// i: 0, x: 1

-=

i = 1
x = i -= 1 // shorthand of i = i - 1, equals to i--
// i: 0, x: 0

-1

i = 1
x = i - 1 // return i - 1 only and not changing i
// i: 1, x: 0

Refrence: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators