const myfunc = (add1, add2) => {
  return new Promise((resolve, reject) => {
    const new_value = add1 + add2;
    setTimeout(() => {
      resolve(new_value);
    }, 3000);
  })
};

myfunc(1, 5)
  .then((added_value) => {
    console.log(`the value is ${added_value}`);
  })
  .catch((err) => {
    console.error(`there was an error ${err}`);
  });
//-------------------------------
const myfunc = (add1, add2) => {
  return new Promise((resolve, reject) => {
    const new_value = add1 + add2;
    setTimeout(() => {
      console.log(`new value ${new_value}`);
      resolve(new_value);
    }, 3000);
  })
};

const mypromises = [
  myfunc(1, 5),
  myfunc(6, 5),
  myfunc(2, 9),
  myfunc(10, 5),
];

Promise.all(mypromises)
  .then(() => {
    console.log('they all resolved');
  });