What is the behavior of typing {a:1} giving 1, and {a:1, b:2} giving an error in a Javascript console?

The following will show in Firebug or in jsconsole.com or in other Javascript interactive console:

>>> foo = { a : 1, b : 2.2 }
Object { a=1, more...}

>>> foo.a
1

>>> foo.b
2.2

>>> { a : 1, b : 2.2 }
SyntaxError: invalid label { message="invalid label", more...}

>>> { a : 1 }
1

why is the 1 returning for {a : 1} and why is {a : 1, b : 2.2} giving an error? In Ruby, they would come back the same way you defined it.