JavaScript and Objects CS 4640 Programming Languages for Web Applications

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1 JavaScript and Objects CS 4640 Programming Languages for Web Applications 1

2 Objects How group do variables Web and Apps functions fit to create in with a model the World Around Them? representing something you would recognize from the real world Object type: Hotel Event Happens when Method called Reserve reservation is made makereservation() Cancel reservation is cancelled cancelreservation() Method makereservation() cancelreservation() checkavailability() What it does increases value of bookings property decreases value of bookings property subtracts value of bookings property from value of rooms property and returns number of rooms available Object type: Car Event Happens when Method called Break driver slows down changespeed() Accelerate driver speeds up changespeed() Method changespeed() What it does Events are things or interactions that can happen to the objects Methods represent tasks that are associated with the objects (or things we can do with the objects) increases or decreases value of currentspeed property Properties Name: Awesome Rating: Rooms: 5 70 Bookings: 56 Pool: true Gym: true Properties tell us the characteristics of the objects Properties Make: UVA1 currentspeed: 30 Color: yellow Fuel: gasoline 2

3 JavaScript Objects JavaScript is an object-based language, not object-oriented It has and uses objects, but does not support some features necessary for object-oriented languages (such as inheritance and polymorphism) Objects are represented as property-value pair The property values can be data or functions (methods) A property is something that can be modified : Data properties : primitive values or references to objects Method properties : can be executed Objects can be created and their properties can be changed dynamically JS is not really typed.. If it doesn t care between a number and a string, why care between two kinds of objects? 3

4 Creating Objects Create an object and assign variables and functions directly by using { } syntax 4

5 Creating Objects with Constructors Create an instance of the object using the constructor function and the new keyword 5

6 Accessing Objects Access properties or methods of an object using dot notation Access properties or methods using square brackets 6

7 Updating Properties Update properties using dot notation Update properties using square brackets 7

8 Adding Properties Add a property using a dot notation 8

9 Deleting Properties Delete a property using the delete keyword 9

10 Web Browsers and Objects Revisit Object type: Window Properties Location: Properties Object type: Document URL: lastmodified: 01/02/201710:19:23 Title: CS 4640 (Programming Languages for Web Apps) 10

11 BOM: Browser Object Model Revisit BOM collection of objects that the browser makes available to us for use with JavaScript window Object location Object history Object document Object navigator Object screen Object DOM form Object link Object image Object 11

12 DOM: Document Object Model Revisit Properties Event Load Click Keypress Method write() getelementbyid() Object type: Document URL: lastmodified: 01/02/201710:19:23 Title: CS 4640 (Programming Languages for Web Apps) Happens when page and content have finished loading user clicks the mouse over the page user presses down on a key What it does adds content to the document accesses an element of a given id attribute 12

13 How A Browser See A Web Page Revisit document <html> The browser receives an HTML page <head> <meta> <title> <link> http-equiv contenttype Content text/html... CS 4640 (Programming Language for Web Applications) rel stylesheet href styles/cs4640 -style.css... <a> name top width 75% align center align center width 100% size +2 <font> <table> <strong> <tr> <td> <body> size +2 color red <font> It creates a model of the page and stores it in memory It shows the page on screen using a rendering engine <strong> Syllabus Spring

14 Using BOM Objects (Some Properties) Property window.screenx window.screeny window.location window.document window.history window.history.length window.screen window.screen.width window.screen.height Description X-coordinate of pointer, relative to top left corner of screen (in pixels) Y-coordinate of pointer, relative to top left corner of screen (in pixels) Current URL of window object Reference to document object Reference to history object for browser window or tab, which contains details of the pages that have been viewed in that window or tab Number of items in history object Reference to screen object Accesses width property of screen object Accesses height property of screen object 14

15 Using BOM Objects (Some Methods) Method window.alert( ) window.open(url) window.print( ) window.history.back( ) window.history.forward( ) window.history.go(step) history.pushstate(state, title, url) history.replacestate(state, title, url) Description Create modal dialog box with message (user must click OK button to close it) Open new browser window with the specified URL Tell browser that user wants to print contents of current page (act like user has clicked a print option) Move backward through history Move forward through history Move to specific page from session history (step specifies the number of pages, forward or backward) Create a new entry (or add a URL) at the top of the browser history Modify the current entry (current URL at the top) of the browser history 15

16 Using DOM Objects Not part of HTML or JS Separate rules implemented by all major browser markers Two primary purposes: Making a model of the HTML page Specifies how browsers should create a model of an HTML page Accessing and change the HTML page Specifies how JS can access and update the contents of a web page 16

17 DOM: Four Types of Nodes Element node document <html> Document node <head> <body> <meta> <title> <link> <a> <table> http-equiv contenttype Content text/html... CS 4640 (Programming Language for Web Applications) rel stylesheet href styles/cs4640 -style.css... name top align center width 100% <tr> <td> width 75% align center <font> <font> Text node Attribute node size +2 <strong> size +2 color red <strong> Syllabus Spring

18 Using DOM Objects (Some Properties and Methods) Property document.title document.lastmodified document.url document.domain Description Title of current document Date on which document was last modified String containing URL of current document Domain of current document Method document.write( ) document.getelementbyid(id) document.queryselectorall(sel ector) document.createelement(elem ent) document.createtextnode(text) Write text to document Description Return element whose id attribute matches the specified id Return list of elements that match the specified CSS selector Create new element Create new text node 18

JavaScript: Objects, BOM, and DOM CS 4640 Programming Languages for Web Applications

JavaScript: Objects, BOM, and DOM CS 4640 Programming Languages for Web Applications 1 Objects How group do variables Web and Apps functions fit to create in with a model the World Around Them? representing