Why are the number of iterations wrong with this yield generator in javascript?

So here is a code snippet that I am trying to work with.

function* genBubble(arr) {
  for (let i = 0; i < arr.length - 1; i++) {
    for (let j = 0; j < arr.length - i - 1; j++) {
      yield arr; // returning arr after every iteration
      if (arr[j] > arr[j + 1]) {
        swap(arr, j, j + 1); // removed swap for brevity
      }
    }
  }
}
const tempArray = [3, 5, 8, 4, 1, 9, -2];
const genForLoop = genBubble(tempArray);

do {
  console.log(genForLoop.next());
} while (!genForLoop.next().done);

This is a simple bubble sort implementation. As you know bubble sort has n * (n - 1) / 2 iterations, so in this case with array's length being 7, we have 7 * (7 - 1) / 2 iterations which is equal to 21.

But when I run this code, I am only getting 11 iterations. The output is as shown below.

{ value: [ 3, 5, 8, 4, 1, 9, -2 ], done: false }
{ value: [ 3, 5, 8, 4, 1, 9, -2 ], done: false }
{ value: [ 3, 5, 4, 1, 8, 9, -2 ], done: false }
{ value: [ 3, 5, 4, 1, 8, -2, 9 ], done: false }
{ value: [ 3, 4, 5, 1, 8, -2, 9 ], done: false }
{ value: [ 3, 4, 1, 5, 8, -2, 9 ], done: false }
{ value: [ 3, 4, 1, 5, -2, 8, 9 ], done: false }
{ value: [ 3, 1, 4, 5, -2, 8, 9 ], done: false }
{ value: [ 1, 3, 4, -2, 5, 8, 9 ], done: false }
{ value: [ 1, 3, -2, 4, 5, 8, 9 ], done: false }
{ value: [ 1, -2, 3, 4, 5, 8, 9 ], done: false }

I am using node test.js to run this program(test.js is the file where this program is written in).

Note: I do not want to print the array after each iteration. I want to return it. If that helps.

Your main problem is that you're calling next twice, but ignoring the value from every other call. Instead, call it once and remember the result:

let result;
while (!(result = genForLoop.next()).done) {
  console.log(result.value.join(","));
}

...or rather more simply, use for-of (which means you don't have to have the genForLoop identifier):

for (const value of genBubble(tempArray)) {
  console.log(value.join(","));
}

But (I haven't done a bubble sort in years) I believe your inner loop termination needs to be j < arr.length - 1, not just j < arr.length - i - 1. I do vaguely recall that the inner loop can be shorter, but not apparently in that way.

Live Example:

function swap(arr, i1, i2) {
  const t = arr[i1];
  arr[i1] = arr[i2];
  arr[i2] = t;
}
function* genBubble(arr) {
  for (let i = 0; i < arr.length - 1; i++) {
    for (let j = 0; j < arr.length - 1; j++) {
      yield arr; // returning arr after every iteration
      if (arr[j] > arr[j + 1]) {
        swap(arr, j, j + 1); // removed swap for brevity
      }
    }
  }
}
const tempArray = [3, 5, 8, 4, 1, 9, -2];

for (const value of genBubble(tempArray)) {
  console.log(value.join(","));
}

.as-console-wrapper {
  max-height: 100% !important;
}

Your outer loop condition should be < arr.length, not < arr.length - 1.