When I do new String("hello") in my console I get the following result:
String {"hello", length: 5}
The first value in the String Object that was returned doesn't have a key.
Since objects are associative/hash arrays i.e. defined and created with keys and values how is the String constructor returning an object with a value without key?
It doesn't.
You're just misinterpreting the console's visualisation of a string object and assuming it is expressing it in the form of object literal syntax. If it would, you would see:
{ 0: "h", 1: "e", 2: "l", 3: "l", 4: "o", length: 5, __proto__: String }
But thats certainly quite unreadable, so they probably changed the way of visualizing to make it easier to read.
length: 0? But still: what you see in the console is not always what the objects look like in js