The purpose of the clone() method is to allow reuse of the (normally single-use) Body of the request. Unfortunately, the implementation in this polyfill doesn't allow that.

To illustrate the problem, this example code will fail:

var r1 = new Request('http://somewhere.com', { method: 'POST', body: 'test' });
var r2 = r1.clone();
r1.text(); // --> fails - but should succeed
r2.text(); // --> succeeds

The clone() method in this polyfill just delegates to the constructor, but the constructor is supposed to consume the stream of the original request (which it does), and the clone() method is supposed to leave it untouched.