Destructuring assignment in while loop in ES6 function doesn't propogate out of loop?

Question

I was implementing a simple GCD algorithm in ES6 (through node-esml) and came upon (to me) strange behaviour with updating values of variables inside a while loop. This code

Answer 1

That's a problem not with destructuring assignment, but with ASI (automatic semicolon insertion). These two lines:

q = Math.floor(rdash / r)
[r, rdash] = [rdash - q * r, r]

in practice mean this:

q = Math.floor(rdash / r)[r, rdash] = [rdash - q * r, r]

which obviously is not what you meant. To fix that, add a semicolon in front of [:

function gcdWithDestructuredAssignment(x, y) {
  let [r, rdash] = [x, y]
  while (r != 0) {
    q = Math.floor(rdash / r)
    ;[r, rdash] = [rdash - q * r, r]
  }
  return(rdash)
}
console.log(gcdWithDestructuredAssignment(97, 34))

Of course you can add the missing semicolon at the end of the previous line instead (q = Math.floor(rdash / r);), but since you generally don't use semicolons, I assumed that you're using npm coding style.