Using the FileReader API in async functions

readFileAsync.js

// https://simon-schraeder.de/posts/filereader-async/

function readFileAsync(file) {
  return new Promise((resolve, reject) => {
    let reader = new FileReader();

    reader.onload = () => {
      resolve(reader.result);
    };

    reader.onerror = reject;

    reader.readAsArrayBuffer(file);
  })
}

async function processFile() {
  try {
    let file = document.getElementById('fileInput').files[0];
    let contentBuffer = await readFileAsync(file);
    console.log(contentBuffer);
  } catch(err) {
    console.log(err);
  }
}