async.generator.body.js

const getValue = () => { console.log('get-value'); return 'value'; };

async function* foo(value = getValue()) {
  console.log('before yield', value);
  yield value + '-yiled';
  
  console.log('after yield');
  return value + '-result';
}

async function boo() {
  const iter = foo();
  console.log('before iteration');
 
  let result = await iter.next();
  console.log('step1:', result.value, result.done);
  
  result = await iter.next();
  console.log('step2:', result.value, result.done);
}

boo();

// get-value
// before iteration
// before yield value
// step1: value-yiled false
// after yield
// step2: value-result true