Sometimes you want to get an updated property . In this case, I am animating an image to make it 10% bigger when I hover over it. I also have a slider that allows the grid sizing to change.

$(img.currentTarget).animate({
    'position': 'absolute',
    'height': (function() { return $('#slider').slider('value') * 1.1 + '%' })(),
    'width': (function() { return $('#slider').slider('value') * 1.1 + '%' })(),
    'z-index': '10',
    'margin': '-15px -15px -15px -15px'},
    0,
    function() {}
})

Here I am replacing a static property with a function that can return new information. It is still accessed in the same way but behaves the way I wanted.