How to make async/await output to a file in the correct order?

Question

Node.js

let data = {cat:1,dog:2};
Object.keys(data).map(async (id) => {
                await  appendFile(fileName, id);
                await  appendFile(fileName, data[id]);
        });

out: catdog12
But i want:
cat1dog2

Answer 1

async function saveData(data) {
  for(let id of Object.keys(data)) {
    await  appendFile(fileName, id);
    await  appendFile(fileName, data[id]);
  }
}

saveData({cat:1,dog:2})

As an option, for sequential execution, solve the problem purely on promises:

let data = {cat:1,dog:2};
Object.keys(data).reduce(
  (p, id) => p
    .then(() => appendFile(fileName, id))
    .then(() => appendFile(fileName, data[id])),
  Promise.resolve()
);