Javascript sorting with generators

// HTML for this example: <pre id="output"></pre>

function compare(a/*: number*/, b/*: number*/)/*: ['compare', number, number]*/ {
    return ['compare', a, b];
}
function swap(a/*: number*/, b/*: number*/)/*: ['swap', number, number]*/ {
    return ['swap', a, b];
}

function* bubbleSort(from/*: number*/, to/*: number*/)/*: Generator<['swap' | 'compare', number, number], void, number> */ {
    let swapped/*: boolean */;
    do {
        swapped = false;
        to -= 1; // decrement by 1 EACH loop, as we know the last element will be in place
        for (let j = from; j < to; j++) {
            if ((yield compare(j, j + 1)) > 0) {
                yield swap(j, j + 1);
                swapped = true;
            }
        }
    } while(swapped);
}

function log(text/*: string*/)/*: void */ {
    console.log(text);
    document.getElementById('output').innerText += text + '\n';
}

function test(array/*: number[] */)/*: void */ {
    const generator = bubbleSort(0, array.length);
    let latestArray = array;
    let nextValue = 0;
    while(true) {
        const action = generator.next(nextValue);
        if(action.done) {
            log(JSON.stringify(latestArray) + ': Done')
            return;
        } else if (action.value[0] === 'compare') {
            const a = latestArray[action.value[1]];
            const b = latestArray[action.value[2]];
            if(a > b) {
                nextValue = 1;
            } else if (a < b) {
                nextValue = -1;
            } else {
                nextValue = 0;
            }
            log(JSON.stringify(latestArray) + `: Compared ${action.value[1]}: ${a} to ${action.value[2]}: ${b} resulting in ${nextValue}`);
        } else if (action.value[0] === 'swap') {
            latestArray = [...latestArray]
            const tmp = latestArray[action.value[1]];
            latestArray[action.value[1]] = latestArray[action.value[2]];
            latestArray[action.value[2]] = tmp;
            log(JSON.stringify(latestArray) + `: Swapped index ${action.value[1]} and ${action.value[2]}`);
        } else {
            throw new Error('What? ' + JSON.stringify(action.value));
        }
    }
}
const array = [9, 3, 4, 0, 7, 5, 2, 8, 1, 6];
test(array);