What function can be used to alternate an element's state between display and hidden?

Which is the correct command to fade in an element over a three-second time period?

Which is valid?

Illustrate selecting a HTML element using its class:

Which is a syntactically valid jQuery command?

Which function does jQuery provide to remove whitespace from the beginning and end of a string?

Though jQuery offers visual effects, it is considered a best practice to use CSS to set up different states triggered by classes, where it makes sense. What's the easiest way to enable and disable a class bounce on an element with the ID dialog?

Effects like show, hide, fadIn, and fadeOut can be called with no arguments, but can also take arguments for how long they should last. Which is NOT a duration argument supported by these functions?

What is tricky about jQuery's nth- filters (:nth-child, :nth-of-type, etc.) relative to other filters?

You want to work with AJAX using a Promise-like interface instead of nested callback functions. What jQuery API should you use?

When writing jQuery plugins, we often provide default options that may be overridden by the end user. What jQuery function is most useful for this purpose?