for-await-await-using-of-await-1.js

import { setTimeout } from 'timers/promises';

/**
 * @param {number} n
 */
async function range(n) {
    let i = 0;
    await setTimeout(100 * Math.random());
    return {
        [Symbol.asyncIterator]() {
            return {
                async next() {
                    await setTimeout(100 * Math.random());
                    i++;
                    return {
                        value: {
                            i,
                            async [Symbol.asyncDispose]() {
                                await setTimeout(1000 - 500 * i);
                                console.log('asyncDispose', i);
                            },
                        },
                        done: i >= n,
                    };
                },
            };
        },
    };
}

for await (await using x of await range(3)) {
    console.log('x.i =', x.i);
}
/*
output:
x.i = 1
asyncDispose 1
x.i = 2
asyncDispose 2
*/

for-await-await-using-of-await-2.js

let i = 0;
for await (await using x of await ({
    then(onFulfilled) {
        onFulfilled({
            [Symbol.asyncIterator]() {
                return {
                    next() {
                        return {
                            value: {
                                [Symbol.dispose]() { console.log('dispose', i++) }
                            },
                            done: i > 2
                        }
                    }
                }
            }
        });
    }
})) {}