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Manipulating the DOM

Manipulating the DOM. CST 200 – JavaScript 3 – 4 - 13. Objectives. Learn how to work with the Document Object Model (DOM) Learn about the various arrays stored within the Document object Work with the document.images[] Array Use the document.getElementById() function

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Manipulating the DOM

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  1. Manipulating the DOM CST 200 – JavaScript 3 – 4 - 13

  2. Objectives • Learn how to work with the Document Object Model (DOM) • Learn about the various arrays stored within the Document object • Work with the document.images[] Array • Use the document.getElementById() function • Work with the innerHTML property

  3. Document Object Model • The Document Object Model (DOM) is a hierarchy of objects that represent the web browser, the web page document and web page elements • The DOM provides programmatic access to different aspects of the Web browser window and Web page

  4. Document Object Model

  5. Document Object Model (cont) • Objects in the Document Object Model (DOM) are created automatically by the web browser when the web browser opens a page • The top-level object is the Window object, which represents the browser window

  6. Window Object • TheWindowobject represents a Web browser window • The Window object is called the global object because all other DOM objects are contained inside of it • We've used the Window object to display pop-up boxes to the user window.alert(msg);

  7. The Document Object • The Document object represents the Web page displayed in a browser • The Document objects contains all the Web page elements • Each web page element is further represented as its own object • We've used the Document object to write information to the web page document.write(msg);

  8. Document Object Arrays • The Document object contains arrays to store and organize specific html elements • Each array stores a specific category of html elements • These arrays include: • anchors[ ] • applets[ ] • forms[ ] • elements[ ] • images[ ] • links[ ] the images[ ] array stores Image objects corresponding to each <img> element

  9. Accessing DOM Objects Consider the page below, containing one <h2> element and three <img> elements: <body> <h2>Letters</h2> <img src="A.jpg" alt="A" /> <img src="B.jpg" alt="B" /> <img src="C.jpg" alt="C" /> </body>

  10. Accessing DOM Objects (cont) • When the web browser loads the page, each a new Image object will be created to represent each <img> element • The document.images[] array will store all of the Image objects document.images[0] document.images[1] document.images[2]

  11. Accessing DOM Objects (cont) • The first element of the document.images[] array is an Image object document.images[0] • This Image object has properties and methods that can be accessed

  12. Accessing Object Properties • Once identifying a specific object, we can then access specific properties • document.images[0]is the first Image object • We can access properties of theimage, such as document.images[0].src document.images[0].width document.images[0].height src = "A.jpg" height = 240 width = 240

  13. Web Console Exercise #1 • Open the following page in Firefox:http://www.capitalcc.edu/faculty/sfreeman/cst200/dom/letters.html • Enter the following expressions into Web Console. What does each statement return? document.images[0] document.images[0].src document.images[0].width document.images[0].border document.images[1] document.images[1].height

  14. Accessing DOM Objects (cont) • Another way of accessing DOM objects is by assigning the name attribute to html elements • Below we set the name attribute to the images: <imgsrc="A.jpg" name="imgA" alt="A"/> <imgsrc="B.jpg" name="imgB" alt="B"/> <imgsrc="C.jpg" name="imgC" alt="C"/>

  15. Accessing DOM Objects (cont) Elements can then be referenced by adding the name following a period(.), following the document object document.imgA document.imgB document.imgC

  16. Accessing DOM Objects (cont) Using the DOM, we can access the same Image object, in two different ways: Through the element's name: document.imgA or through the images[ ] array document.images[0]

  17. Modifying Object Properties • We can also modify the object properties by assigning a new value to a property // set a new file as the image src document.images[0].src= "newA.jpg"; // set a new image width document.images[0].width = 500; // set a new border width document.imgA.border = 5; // hide image by changing the css display // property document.imgA.style.display="none"

  18. Web Console Exercise #2 • Return to the letters.html web page in Web Console • Enter the following statements into Web Console. What does each statement do? document.imgA.src = "B.jpg" document.imgA.width = 50 document.imgA.width = 350 document.imgA.border = 15 document.imgA.src = "A.jpg" document.imgB.style.display = "none"

  19. Accessing DOM Object - Exercise • Assume the following page: <html> <body> <h2>Welcome Guests</h2> <imgsrc="porch.jpg" name="homePorch"/> <p>Guests can check in anytime after 8pm</p> <imgsrc="creek.jpg" name="creek"/> </body> </html> • Write down how to access the creek Image object through the images[ ] array and through the element name.

  20. Accessing JavaScript Objects (cont) • So far, we have accessed objects through the Document object and images[] array • When referring to the current object, another way of accessing an object is through the this keyword • The this keyword refers to the current object • Example: <img src="creek.jpg" alt="shallow creek" onclick="window.alert('This image is located at the following URL: ' + this.src);" />

  21. Accessing JavaScript Objects (cont) • Using the this keyword, we can easily manipulate the current object <img src="A.jpg" alt="A" onmousedown="this.src='B.jpg'" onmouseup="this.src='A.jpg'" /> <imgsrc="B.jpg" alt="B" onmouseover="this.border=20" onmouseout="this.border=0" />

  22. getElementById() function • We've seen two ways of accessing a DOM object through the document array and with the name attribute value • Another way of accessing a specific DOM object is with the document.getElementById() function JavaScript, Fifth Edition

  23. getElementById() function (cont) • The document.getElementById( ) function returns a DOM object based on the id attribute • In order to use this function, the html element must have been assigned an id attribute JavaScript, Fifth Edition

  24. getElementById() example Example: imagine in our html document we defined the following element: <img src="boy.jpg" name="john" id = "john" /> We can then use the JavaScript expression: document.getElementById("john") to access the DOM object representing the element JavaScript, Fifth Edition

  25. getElementById() example #2 document.getElementById("top") <body> <h1 id="top">Intro</h1> <div id="main" > <p id="welcome" > Welcome to the … </p> </div> <div id="footer"> </div> </body> document.getElementById("welcome") document.getElementById("main") document.getElementById("footer") JavaScript, Fifth Edition

  26. Web Console Exercise #3 • Return to the letters.html web page in Web Console • Enter the following statements into Web Console. What does each statement do? document.getElementById("letters") document.getElementById("summary") document.getElementById("img5") document.getElementById("img5").width

  27. innerHTML property • Each html element has an innerHTML property that can be used to change the content of the html element • Setting the innerHTML property to a value, will update the content of the html element • We will use innerHTML in conjunction with document.getElementById() JavaScript, Fifth Edition

  28. innerHTML property (cont) Example: imagine in our html document we defined the following element: <p id="welcome" >Welcome to Bill’s Auto</p> We can then use the JavaScript expression: document.getElementById("welcome").innerHTML to access the content of the paragraph element JavaScript, Fifth Edition

  29. Web Console Exercise #3 • Return to the letters.html web page in Web Console • Enter the following statements into Web Console. What does each statement do? document.getElementById("summary").innerHTML= “Welcome to Letters Page” document.getElementById("contact").innerHTML= “Contact Us “

  30. Summary • Document object model (DOM) is a hierarchy of objects representing web page elements • Document object represents the web page, and contains all web page elements • Document object contains arrays that can be used to identify Web page elements • JavaScript can reference any Web page element through the DOM JavaScript, Fifth Edition

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