Value returned by the assignment

Question

Why does the regular assignment statement (say, x = 5) return the value assigned (5 in this case), while the assignment combined with a variable d

Answer 1

That's because var x = 5; is a variable statement, not an expression.

The behaviour of this statement is described in Section 12.2 of the ECMAScript Language Reference.

1. Evaluate VariableDeclarationList.
2. Return (normal, empty, empty).

This is basically a void return value.