Support FormData file

[hthetiot]

var file = new File(["foo"], "foo.txt", {
  type: "text/plain",
});

var formData = new FormData();
formData.append("username", "Groucho");
formData.append("accountnum", 123456); // number 123456 is immediately converted to a string "123456"
formData.append("userfile", file);

var pairEntry, iterator = formData.entries();
var loader = new FileReader();

while (
    (pairEntry = iterator.next()) &&
        pairEntry.done === false
) {
    var value = pairEntry.value[1],
        key = pairEntry.value[0];

    console.log(key, value, typeof value);
}

var loader = new FileReader();
loader.onload = function (loadEvent) {
    console.timeEnd(file);
};
console.time(file);
loader.readAsText(file);

Reference:

• https://stackoverflow.com/questions/14438187/javascript-filereader-parsing-long-file-in-chunks
• https://bugs.chromium.org/p/chromium/issues/detail?id=349304