Distinguish Entry in FormData - File or string

Question

I am accessing a FormData (LINK) value which is of

type FormDataEntryValue = File | string;

.

What is a safe method to determine whether the value is a File or string?

Answer should obviously not include as, any, ..

Answer 1

Use narrowing.

const val: FormDataEntryValue = ...
if (typeof val === 'string') {
  // type is inferred to be a string
} else {
  // type is inferred to be a File
}