Creating Animations, Working with Graphics, and Accessing Data Lesson 9

Exam Objective Matrix Skills/ConceptsMTA Exam Objectives Coding Animations by Using JavaScript Code animations by using JavaScript. (4.3) Working with Images, Shapes, and Other Graphics Code animations by using JavaScript. (4.3) Sending and Receiving DataAccess data access by using JavaScript. (4.4) Loading and Saving FilesAccess data access by using JavaScript. (4.4) Using JavaScript to Validate User Form Input Access data access by using JavaScript. (4.4) Understanding and Using Cookies Access data access by using JavaScript. (4.4) Understanding and Using LocalStorage Access data access by using JavaScript. (4.4)

Animation Animation is the display of a sequence of static images at a fast enough speed to create the illusion of movement. Regarding the user interface, animation has to do with changing a display to make it dynamic—not just a one-time change but a seamless one. JavaScript can produce spectacular animation effects.

Recursion Recursion is a programming technique in which a function calls itself. Recursion is a key part of animation. The most effective way to introduce a “timing element” into JavaScript is to use setTimeout recursively. –Have it invoke another execution of the same function from which the setTimeout() was called.

A Simple Animation Example

A Simple Animation Example (Continued)

createElement Method You can use the JavaScript createElement method to display an image when a button is clicked or some other event occurs.

Canvas Element To draw a canvas object, use: –getElementById() function to find the canvas element –canvas.getContext to create the canvas object Then use a variety of methods to draw shapes, include images, and so on.

Canvas Example: Analog Clock

Canvas Example: Analog Clock (Continued)

Sending and Receiving Data One of the most essential techniques for data transfer involves the XMLHttpRequest API. –Sometimes abbreviated as XHR XMLHttpRequest enables you to use JavaScript to pass data in the form of text strings between a client and a server.

XMLHttpRequest General syntax:

XMLHttpRequest The XMLHttpRequest object creates a call to the server. The open method specifies the HTTP method for contacting the server and provides the server’s Web address. The callback function gets a response from the server. xhr.send(data) sends the data.

Accessing Data Example

Parsing Parsing is a term used to describe analysis of complex information into constituent parts. Use parsing for extracting information from a data stream of stock quotes and similar tasks.

Parsing Example

JSON You can also use JSON.parse and JSON.stringify APIs to exchange JavaScript objects with a server.

Loading and Saving Files JavaScript can access files on a local computer and, using HTML5, validate the file type before loading, which greatly reduces errors.

Access a Local File Example

Access a Local File Example (Continued)

Application accepts image files but not other formats

Access a Local File Example (Continued) Application accepts image files but not other formats

AppCache AppCache saves a copy of Web site files locally, in a structured form. AppCache is not the same as a browser’s cache. Whereas a browser’s cache saves all Web pages visited, AppCache saves only the files listed in the cache manifest.

AppCache Example

Data Types A data type is JavaScript’s interpretation of the kind of data a program can work with. Data types include: – string –Number –Array –Boolean –Null –Object –undefined

User Input Form Validation As end users enter data in a form, JavaScript can instantly validate entries and suggest alternatives.

Client-side Validation Example

Client-side Validation Example (Continued)

Cookies Cookies are small text files that Web sites save to a computer’s hard disk that contain information about the user and his or her browsing preferences. The content of cookies change as a user revisits a site and selects different items or changes preferences. In JavaScript, a cookie is a variable. JavaScript can create and retrieve cookies.

Use Cookies Example

Local Storage HTML5’s Local Storage feature has better security and makes programming easier than with cookies.

Recap Animation Recursion createElement method Canvas Sending and receiving data XMLHttpRequest API Accessing a local file AppCache Data types User input form validation/client-side validation Cookies Local Storage