I have looked through Simon Willison’s Re-Introduction to JavaScript several times, and have found this apt explanation of the object literal semantics only now:

"There are two basic ways to create an object:

var obj = new Object();

And:

var obj = {};

These are semantically equivalent; the second is called object literal syntax, and is more convenient. Object literal syntax was not present in very early versions of the language which is why you see so much code using the old method."