The FormData object allows pages to programmatically construct a list of key/value entries that can be submitted via XHR just like an HTML form. Previously, the object was write-only via a single append() method. The spec was fleshed out to add has(), get(), getAll(), delete(), set(), entries(), keys(), values(), forEach() and Symbol.iterator() methods to allow inspection, iteration and modification.
Docs: https://developer.mozilla.org/en-US/docs/Web/API/FormData https://developers.google.com/web/updates/2016/03/formdata-methods-for-inspection-and-modification
Samples: https://googlechrome.github.io/samples/formdata-methods/index.html