Creating Animations, Working with Graphics, and Accessing Data

Lesson 9

Exam Objective Matrix

Skills/Concepts MTA 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 Data

Access data access by using JavaScript. (4.4)

Loading and Saving Files Access 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)

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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.

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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. 4

A Simple Animation Example

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A Simple Animation Example (Continued)

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A Simple Animation Example (Continued)

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

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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.

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Canvas Example: Analog Clock

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Canvas Example: Analog Clock (Continued)

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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.

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XMLHttpRequest

• General syntax:

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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.

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Accessing Data Example

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Accessing Data Example

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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.

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Parsing Example

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Parsing Example

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

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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.

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Access a Local File Example

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Access a Local File Example (Continued)

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

other formats

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

other formats

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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.

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AppCache Example

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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

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User Input Form Validation• As end users enter data in a form,

JavaScript can instantly validate entries and suggest alternatives.

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Client-side Validation Example

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Client-side Validation Example (Continued)

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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.

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Use Cookies Example

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Local Storage• HTML5’s Local Storage feature has

better security and makes programming easier than with cookies.

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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

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