Improve documentation for FormDataLike interface.

Author: octet-stream

lib/FormDataLike.ts

@@ -1,20 +1,45 @@
 import {FileLike} from "./FileLike"
 
 /**
- * This interface reflects possible values of each FormData entry
+ * A `string` or `File` that represents a single value from a set of `FormData` key-value pairs.
  */
 export type FormDataEntryValue = string | FileLike
 
 /**
  * This interface reflects minimal shape of the FormData
  */
 export interface FormDataLike {
-  append(name: string, value: unknown, filename?: string): void
+  /**
+   * Appends a new value onto an existing key inside a FormData object,
+   * or adds the key if it does not already exist.
+   *
+   * The difference between `set()` and `append()` is that if the specified key already exists, `set()` will overwrite all existing values with the new one, whereas `append()` will append the new value onto the end of the existing set of values.
+   *
+   * @param name The name of the field whose data is contained in `value`.
+   * @param value The field's value. This can be [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob)
+    or [`File`](https://developer.mozilla.org/en-US/docs/Web/API/File). If none of these are specified the value is converted to a string.
+   * @param fileName The filename reported to the server, when a Blob or File is passed as the second parameter. The default filename for Blob objects is "blob". The default filename for File objects is the file's filename.
+   */
+  append(name: string, value: unknown, fileName?: string): void
 
+  /**
+   * Returns all the values associated with a given key from within a `FormData` object.
+   *
+   * @param {string} name A name of the value you want to retrieve.
+   *
+   * @returns An array of `FormDataEntryValue` whose key matches the value passed in the `name` parameter. If the key doesn't exist, the method returns an empty list.
+   */
   getAll(name: string): FormDataEntryValue[]
 
+  /**
+   * Returns an [`iterator`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) allowing to go through the `FormData` key/value pairs.
+   * The key of each pair is a string; the value is a [`FormDataValue`](https://developer.mozilla.org/en-US/docs/Web/API/FormDataEntryValue).
+   */
   entries(): Generator<[string, FormDataEntryValue]>
 
+  /**
+   * An alias for FormDataLike#entries()
+   */
   [Symbol.iterator](): Generator<[string, FormDataEntryValue]>
 
   [Symbol.toStringTag]: string