Having problems with anonymous functions in JavaScript

Question

jQuery.fn.testeee = function(_msg)
{
    alert(_msg);
    $(this[0]).overlay({ 
        onBeforeLoad: function() 
        {
            alert(_msg);
        }
    }).load();
};
$("#popup").testeee ('test');
$("#popup").testeee ('another_test');

This displays:

test
test
another_test
test

The alert() inside de anonymous function asigned to onBeforeLoad keeps showing "test". I try this:

jQuery.fn.testeee = function(_msg)
{
    alert(_msg);
    $(this[0]).overlay({ 
        onBeforeLoad: static_func(_msg)
    }).load();
};
function static_func(_msg) 
{
    alert(_msg);
}
$("#popup").testeee ('test');
$("#popup").testeee ('another_test');

And it works just fine. It displays:

test
test
test
test

Anybody knows why can be happening this?

What happens when you call testeee on different elements? Perhaps overlay doesn't create a new one if there's already one on the element? — seth
– seth, Commented Sep 9, 2009 at 5:24

Guffa · Accepted Answer · 2009-09-09 05:30:53Z

2

If you create an object like this:

{
   onBeforeLoad: static_func(_msg)
}

It doesn't specify a function to call, instead it calls the function immediately and stores the return value in the object.

To specify a function to call you only use the function name:

{
   onBeforeLoad: static_func
}

If you want to call the function with a parameter that you specify yourself, you have to create a closure that contains the variable by wrapping it in an anonymous function:

{
   onBeforeLoad: function() { static_func(_msg) }
}

answered Sep 9, 2009 at 5:30

Guffa

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1 Comment

user170596 Over a year ago

So, why in the first example the function alert() (which is called by an anonymous function) keeps showing the first value of _msg test instead of showing the value that you are actually passing in the next callings (another_test in this case)?

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