Sams Teach Yourself HTML, CSS & JavaScript Web Publishing in One Hour a Day

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552 LESSON 19: Using JavaScript in Your Pages

Q In what cases might you want to use JavaScript without a library like

JavaScript?

A If your JavaScript is very simple, it may be worth it to leave out supporting librar-

ies. But for most web developers, starting with a tool that accounts for differ-

ences between browsers is a great way to avoid bugs and get things done quickly

and simply. It’s generally better to make use of these sorts of libraries to write

JavaScript from scratch. It’s a good idea to know how to write JavaScript without

libraries, but using them almost always makes sense.

Quiz

1. What happens whenever a user clicks a link, button, or form element on a web
   page?


2. In an event handler, what does this refer to?


3. What kinds of nodes on a page can be associated with properties like nextChild
   and previousChild?


4. How does form validation with JavaScript conserve server resources?

Quiz Answers

1. Whenever a user clicks a link, a button, or any form element, the browser generates
   an event signal that can be captured by one of the event handlers mentioned in the
   previous lesson.


2. In event handlers, this is a reference to the element on which the event was called.
   So in an event handler for the onclick event of a link, this would refer to the link
   that the user clicked on.


3. Nodes in the DOM can include HTML elements, text inside HTML elements, and
   even whitespace between elements.


4. JavaScript enables you to do error checking in forms on the browser side before
   the form is ever submitted to the server. A script must access the server before
   it can determine the validity of the entries on a form. (Note that even if you use
   JavaScript form validation, you must validate user input on the server, too, because
   users can bypass the JavaScript if they choose.)