Why this kind of function invocation is wrong in JavaScript?

Question

I\'d like to create an anonymous function and then invoke it immediately.

1) This will bring a syntax error. Why?

function ()
{
    alert(\"hello\");         


        

Answer 1

The ECMAScript Language Specification, section 12.4, says:

An ExpressionStatement cannot start with the function keyword because that might make it ambiguous with a FunctionDeclaration.

So your case 1 is not allowed, because it might lead to ambiguities in the language. The other cases are different kinds of statements (not ExpressionStatements) in which this is not a problem, so the construct is allowed there.