How to inspect FormData?

I’ve tried console.log and looping through it using for in.

Here it the MDN Reference on FormData.

Both attempts are in this fiddle.

var fd = new FormData(),
    key;

// poulate with dummy data
fd.append("key1", "alskdjflasj");
fd.append("key2", "alskdjflasj");

// does not do anything useful
console.log(fd);

// does not do anything useful   
for(key in fd) {
    console.log(key);
}

How can I inspect form data to see what keys have been set.