Question

This code in the book jQuery in action, on page 156.

I don’t understand this part:

{opacity:'toggle'}

Can toggle be an opacity value?

$.fn.fadeToggle = function(speed){
return this.animate({opacity:'toggle'},speed);
};

Answer 1

From the documentation:

In addition to numeric values, each
property can take the strings ‘show’,
‘hide’, and ‘toggle’. These shortcuts
allow for custom hiding and showing
animations that take into account the
display type of the element.

Using toggle will animate the opacity of the element at the speed you specify — hiding it if it’s visible, showing it if it’s hidden.