javascript - Why does `{foo: 1}` evaluate to `1` in the console, and `{foo: 1, bar: 2}` results in an error?

Question

I knew that {} is either an object or a block of code, but today my co-worker asked me why {foo: 1} works when entered into the console, but {foo: 1, bar: 2} generates an error.

Why does foo: 1 evaluate in the console to 1?

Answer 1

By itself, {a: 1} is a block statement, where a is a label.

Of course, in a context where an expression is expected, it is an object literal:

var o = { a: 1 };