JavaScript V Robin Burke ECT 270

Outline Manipulating style Special effect examples

Manipulating style We can manipulate style dynamically just like other element properties Each element has an associated style object setting the properties of this object change the element's displayed style editing embedded style

Manipulating element class Instead of changing style directly change an element's class let CSS define the transformation Benefit style information not buried in JavaScript elem.className = 'new class' why not elem.class?!

Example class-based rollover expandable outline

Visibility Style property controls whether an element is shown on the page Why would I want to hide content? so I can show it later, dynamically

Controlling visibility Visibility elem.style.visibility = "hidden"; or "visible", "inherit" element takes up space but can't be seen elem.style.display = "none"; or "" element takes up no space

Example validation

Modifying a style associated with a class Stylesheets themselves are objects Accessed via styleSheets[] array Each style sheet has an array of rules cssRules[] (NS) rules [] (IE) We can inspect and modify the styles change affects every element using the style

Example rollover

Manipulating position and boundary Position is another style property also boundary via clip property Many effects possible animation drop down menus

Implementation Relevant DOM properties elem.style.left elem.style.top Problem these are string values with units "5 px", "10 in" Solution IE-specific elem.style.pixelLeft integer valued use text processing parseInt to get value value + "px" to set

Animation Repeated display with transformation Example animation loop repeat until animation ended draw current frame delay change frame

Animation, cont'd Problem looping wastes computer resources worse, prevents user interaction Solution "animation callback" uses JavaScript event mechanism

Animation callback Caller sends the name of a function a delay Event mechanism waits as specified by the delay calls the function SetTimeout (fn, delay)

Animation examples linear shift path animation snowflakes

Controlling display Clipping Can set the size of the container smaller than its contents elem.style.clip = rect(x1, y1, x2, y2);

Controlling display, cont'd Clipping creates a viewing area can't access the rest of the image or contents To shrink viewing area, but allow access change size of the element set overflow property

What to do with excess Use overflow property

Drop-down effects Clipping can be used for drop-down menus purely in HTML no images

Before clipping After clipping

Note Book's DOM API is not needed with Mozilla Book's code is really ugly mine is better

Next Week No class Monday Wednesday XML Reading: w3schools tutorial (XML Basic only)