Question

I have a question about Javascript Variable Declare.
Could you please tell me what’s the difference between the following two definition way?
Why the alertMsg will be executed in the 1st way but not in the 2nd way?
Thanks in advance.

//1

var alertMsgInvoker = alertMsg ('hi there');
function alertMsg (msg) {
        alert(msg);
}

//2

var alertMsgInvoker = function () { 
        alertMsg ('hi there');
}
function alertMsg (msg) {
        alert(msg);
}

Answer 1

In your first example you’re assigning the result of calling alertMsg ('hi there'); to the variable alertMsgInvoker. The fact that alertMsg doesn’t return a value to put into alertMsgInvoker is neither here nor there.

In the second example you’re declaring alertMsgInvoker is a function that, when called, calls the function alertMsg. To obtain the same result as in your first example, your second would need to read:

var alertMsgInvoker = function () { 
        alertMsg ('hi there'); 
} 
function alertMsg (msg) {
        alert(msg); 
}

// Now call alertMsgInvoker 
alertMsgInvoker();