How to use Promises with PapaParse?

Question

PapaParse has an asynch callback function for its API. I was wondering how I can convert it to a promise. For eg:

Papa.parse(fileInput.files[0], {
    complete: function(results) {
        console.log(results);
    }
});

Any help would be appreciated!

Crutch

Answer 1

The basic pattern is

Papa.parsePromise = function(file) {
  return new Promise(function(complete, error) {
    Papa.parse(file, {complete, error});
  });
};

Then

Papa.parsePromise(fileInput.files[0]) .
  then(function(results) { console.log(results); });

Pyramidal

This works, and thank you, but I don't understand what complete and error are doing. Could you please explain? – Ruffin

@Ruffin complete is the Promise's resolve function and error is the reject function, they are being used as the callback functions on complete and error for Papa.parse. – Emeritaemeritus

Nice, great job! – Hexagram

Answer 2

If you want to use Async/Await...

someButtonClicked = async rawFile => {
    const parseFile = rawFile => {
      return new Promise(resolve => {
        papa.parse(rawFile, {
          complete: results => {
            resolve(results.data);
          }
        });
      });
    };
    let parsedData = await parseFile(rawFile);
    console.log("parsedData", parsedData);
  };

Hydrosol

You should move the parseFile "helper" function outside of someButtonClicked, it's really independent from the use of async/await there. – Brueghel

Answer 3

I guess it can be used with all kind of variations, I am providing the string to parse although you can use it with file path or url :

  const parseData = (content) => {
  let data;
  return new Promise( (resolve) => {
    Papa.parse(content, {
      header: true,
      delimiter: ',',
      dynamicTyping: true,
      complete: (results) => {
        data = results.data;
        resolve(data);
      }
    });
    
  });
};

Hudson

This is plain wrong and does not work when the complete callback is asynchronous. You resolve the promise before data gets assigned. – Brueghel

ohh sorry that was typo from my side – Hudson

But if you do it properly, you don't need that let data at all – Brueghel