[How trigger file downloads with JavaScript]

download.js

function downloadFile(file) {
  // Create a link and set the URL using `createObjectURL`
  const link = document.createElement("a");
  link.style.display = "none";
  link.href = URL.createObjectURL(file);
  link.download = file.name;

  // It needs to be added to the DOM so it can be clicked
  document.body.appendChild(link);
  link.click();

  // To make this work on Firefox we need to wait
  // a little while before removing it.
  setTimeout(() => {
    URL.revokeObjectURL(link.href);
    link.parentNode.removeChild(link);
  }, 0);
}

// Dynamically create a File
const myFile = new File([`${new Date()}: Meow!`], "my-cat.txt");

// Download it using our function
downloadFile(myFile);