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I'd like to create an anonymous function and then invoke it immediately.
1) This will bring a syntax error. Why?
function ()
{
alert("hello");
}();
2) wrap the function definition with () and it works.
(function ()
{
alert("hello");
})();
3) or, assign the anonymous function to a variable. It works.
var dummy = function()
{
alert("hello");
}();
Why the first way doesn't work?
217
JavaScript Function Invocation is used to executes the function code and it is common to use the term “call a function” instead of “invoke a function”. The code inside a function is executed when the function is invoked.
An "illegal invocation" error is thrown when calling a function whose this keyword doesn't refer to the object where it originally did. In other words, the original "context" of the function is lost.
Never use eval()! eval() is a dangerous function, which executes the code it's passed with the privileges of the caller. If you run eval() with a string that could be affected by a malicious party, you may end up running malicious code on the user's machine with the permissions of your webpage / extension.
The ECMAScript Language Specification, section 12.4, says:
An ExpressionStatement cannot start with the
functionkeyword 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.
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