Responding to keyboard events

This recipe demonstrates how to write an event handler for a common keyboard event, keyup, which is triggered when a key is released. The constructs used in this example are as follows:

Construct	Type	Description
$("#identifier")	jQuery selector	This selects an element using its ID.
$(this)	jQuery object	This refers to the current jQuery object.
.addClass()	jQuery method	This adds the specified CSS class to each matched element.
keyup	jQuery event	This is fired when a key is released. It corresponds to the JavaScript keyup event.
.length	JavaScript property	This returns the length of the string.
.on()	jQuery event binder	This attaches an event handler for one or more events to the matched elements.
.prop(propertyName) or .prop(propertyName, value)	jQuery method	This returns the value of the specified property for the first matched element or sets the value of the specified property for all matched elements.
.substring...