CODEWITHSUNDEEP
javascriptobject
zjy2004ren
zjy2004ren

Reputation: 23

The different way for Javascript Variable Declare

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);
}

Upvotes: 2

Views: 106

Answers (4)

Dave Newton
Dave Newton

Reputation: 160211

You never call a function in the second example. You define some, but never call them.

In the first example you call alertMsg when you define alertMsgInvoker, in the second you define a function that calls alertMsg--but call neither.

Upvotes: 3

nandin
nandin

Reputation: 2575

the first scenario, you are calling function alertMsg which returns undefined.

var alertMsgInvoker = alertMsg ('hi there'); 
// assign the return value (undefined) to variable alertMsgInvoker

the second case, you just defined a variable alertMsgInvoker, which is a function but never get called.

Upvotes: 1

Thomas Johan Eggum
Thomas Johan Eggum

Reputation: 915

In the first scenario you are calling the function alertMsg() with parameter "hi there"; The function is called which fires the alert-function. The function does not return anything, but still you bind the return value of the function to the variable alertMsgInvoker.

In the second scenario, you declare a function to the variabel alertMsgInvoker, then you declare a function named alertMsg. You never fire any of the functions here. That is why the second example doesn`t show the alert-box.

Upvotes: 1

Rob
Rob

Reputation: 45771

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();

Upvotes: 3

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