Unit 2 — The Exciting World of JavaScript Lesson 6 — Using Images with JavaScript

The Exciting World of JavaScript 2 Objectives Understand the names and usage of JavaScript events. Create an image rollover. Make a hyperlink rollover. Build a cycling banner. Display random images. Create a JavaScript slide show.

The Exciting World of JavaScript 3 Making Graphic Images Come Alive Event: This is an operating system response to the occurrence of a specific condition. It can invoke a function. onMouseOut onMouseOver Function: This is a piece of JavaScript written by the programmer that is called upon to perform certain tasks. It can contain any number of JavaScript statements, including calls to other functions or methods.

The Exciting World of JavaScript 4 Making Graphic Images Come Alive (cont.) To make an image rollover, you must – No. 1: Define the variables. HTML and JavaScript var blueArrow = new Image; var redArrow = new Image; blueArrow.src = "bluearrow.gif"; redArrow.src = "redarrow.gif";

The Exciting World of JavaScript 5 Making Graphic Images Come Alive (cont.) No. 2: Write the functions. function turnBlue() { document.arrow.src = blueArrow.src; return; } function turnRed() { document.arrow.src = redArrow.src; return;

The Exciting World of JavaScript 6 Making Graphic Images Come Alive (cont.) No. 3: Describe the events.

The Exciting World of JavaScript 7 Making Graphic Images Come Alive (cont.) Result: the onMouseOver event turns the arrow red and onMouseOut turns the arrow blue.

The Exciting World of JavaScript 8 Event Handling Logic Event handling: JavaScript event statements are placed within standard HTML tags. For example, the onMouseOver and onMouseOut events are located within the opening anchor ( ) tag. These events call the functions turnBlue() and turnRed().

The Exciting World of JavaScript 9 Event Handling Logic (cont.) The turnBlue() and turnRed() functions call: function turnBlue() { document.arrow.src = blueArrow.src; return; } function turnRed() { document.arrow.src = redArrow.src; return; }

The Exciting World of JavaScript 10 Event Handling Logic (cont.) The document.arrow.src = blueArrow.src; and document.arrow.src = redArrow.src; objects have already been assigned. var blueArrow = new Image; var redArrow = new Image; blueArrow.src = "bluearrow.gif"; redArrow.src = "redarrow.gif";

The Exciting World of JavaScript 11 Create a Cycling Banner A cycling banner is really nothing more than a sequence of graphic images that are displayed one after another with a small pause between each image change.

The Exciting World of JavaScript 12 Creating a Cycling Banner (cont.) No. 1: Define the graphics array. <var imgArray = new Array(4); imgArray[0] = new Image; imgArray[0].src = "lions.gif"; imgArray[1] = new Image; imgArray[1].src = "tigers.gif"; imgArray[2] = new Image; imgArray[2].src = "bears.gif"; imgArray[3] = new Image; imgArray[3].src = "ohmy.gif"; var index = 0;

The Exciting World of JavaScript 13 Creating a Cycling Banner (cont.) No. 2: Write the cycle() function. function cycle() { document.banner.src = imgArray[index].src; index++; if (index == 4) { index = 0; } setTimeout("cycle()", 2000); return;

The Exciting World of JavaScript 14 Creating a Cycling Banner (cont.) No. 3: Write the code to trigger the function.

The Exciting World of JavaScript 15 Creating a Cycling Banner (cont.) Result: The graphics cycle every 2000 milliseconds.

The Exciting World of JavaScript 16 Displaying Random Images A cycling banner can display random images one after another with a small pause between each image change.

The Exciting World of JavaScript 17 Displaying Random Images (cont.) No. 1: Define the graphics array. <var imgArray = new Array(4); imgArray[0] = new Image; imgArray[0].src = "lions.gif"; imgArray[1] = new Image; imgArray[1].src = "tigers.gif"; imgArray[2] = new Image; imgArray[2].src = "bears.gif"; imgArray[3] = new Image; imgArray[3].src = "ohmy.gif"; var index = 0;

The Exciting World of JavaScript 18 Displaying Random Images (cont.) Write a select() function. function select() { index = Math.floor(Math.random() * 4); document.banner.src = imgArray[index].src; setTimeout("select()", 2000); return; }

The Exciting World of JavaScript 19 Displaying Random Images (cont.) Write the code to trigger the function.

The Exciting World of JavaScript 20 Displaying Random Images (cont.) Result: Random graphics cycle every 2000 milliseconds.

The Exciting World of JavaScript 21 Creating a JavaScript Slide Show When you allow the user to change the image by clicking on some object with the mouse, the end result is something akin to a slide show.

The Exciting World of JavaScript 22 Creating a JavaScript Slide Show (cont.) No. 1: Define the array. <var imgArray = new Array(4); imgArray[0] = new Image; imgArray[0].src = "lions.gif"; imgArray[1] = new Image; imgArray[1].src = "tigers.gif"; imgArray[2] = new Image; imgArray[2].src = "bears.gif"; imgArray[3] = new Image; imgArray[3].src = "ohmy.gif"; var index = 0;

The Exciting World of JavaScript 23 Creating a JavaScript Slide Show (cont.) No. 2: Write a doBack() function. function doBack() { if (index > 0) { index--; document.slideshow.src = imgArray[index].src; } return; }

The Exciting World of JavaScript 24 Creating a JavaScript Slide Show (cont.) No. 3: Write a doNext() function. function doNext() { if (index < 3) { index++; document.slideshow.src = imgArray[index].src; } return; }

The Exciting World of JavaScript 25 Creating a JavaScript Slide Show (cont.) No. 4: Write the code to trigger the functions. My JavaScript Slide Show Back Next

The Exciting World of JavaScript 26 Creating a JavaScript Slide Show (cont.) Click Next to advance and Back to return to a previous slide.

The Exciting World of JavaScript 27 Summary You can understand the names and uses of JavaScript events. You can create an image rollover. You can make a hyperlink rollover. You can build a cycling banner. You can display random images. You can create a JavaScript slide show.