Programming with JavaScript (Chapter 10)

XP Various things Midterm grades: Friday Winter Career Fair – Thursday, April 28, 2011 (11 am to 3 pm). – MAC Gym, Wade King Student Rec Center – – bring resumes, dress in business attire, and research participating employers in advance.

XP Objectives The script element script Basic JavaScript syntax Write text to a Web page with JavaScript JavaScript data types and variables Create and call a JavaScript function Access an external JavaScript file Add comments to JavaScript code Basic debugging techniques and tools Example of a Javascript applicationJavascript application Examples of document.write()document.write() Lab4 at LAB 3 ANSWERS csci 2023

XP The Development of JavaScript Server-side vs Client-side programming JavaScript is a subset of Java Differences between Java and JavaScript: – Java is a compiled language – JavaScript is an interpreted language JavaScript csci 2024

XP Comparing Java and JavaScript csci 2025

XP The Development of JavaScript Jscript is an IE version of JavaScript ECMA – European Computer Manufacturers Association – develops scripting standards – The standard is called ECMAScript (aka JavaScript) csci 2026

XP Working with the Script Element JavaScript code can either be placed – directly in a Web page file or – saved in an external text file Insert a client-side script in a Web page when using the script element script commands csci 2027

XP Writing Output to the Web Page Object: any item Method: a process by which JS accesses properties of an object To write text to a Web page, use the following JS code: document.write(“text”); or document.writeln(“text”)’ where text is the content to be written to the page. csci 2028

XP Understanding JavaScript Syntax JavaScript is case sensitive Ignores most occurrences of extra white space Do not break a statement into several lines The + symbol used in this command combines several text strings into a single text string csci 2029

XP Declaring a JavaScript Variable Variable: named item designed to store information – JS programs use variables to represent values and text strings You can declare variables with any of the following JavaScript commands: var variable; var variable = value; variable = value; where variable is the name of the variable and value is the initial value of the variable. csci 20210

XP Working with Variables and Data JavaScript variable types: – Numeric variables – String variables – Boolean variables – Null variables You must declare a variable before using it csci 20211

XP Working with Variables and Data Numeric variable: – any number, such as 13, 22.5, etc. – can also be expressed in scientific notation String variable: – any group of characters, such as “Hello” or “Happy Day!” – Must be enclosed within either double or single quotes Boolean variable – accepts only true and false values Null variable – has no value at all csci 20212

XP Working with Variables and Data JavaScript is a weakly typed language The + symbol can be used with either numeric values or text strings var total = 5 + 4; var emLink = "cadler" + + "mpl.gov"; csci 20213

XP Creating a JavaScript Function A function is a collection of commands that performs an action or returns a value A function name identifies a function Parameters are values used by the function The function is executed only when called by another JavaScript command function_name(parameter values) csci 20214

XP Creating a JavaScript Function csci 20215

XP Creating a Function to Return a Value For a function to return a value, it must include a return statement function function_name(parameters){ JavaScript commands return value; } csci 20216

XP Accessing an External JavaScript File The code to access an external script file is: Place all script elements that reference external files in the document head csci 20217

XP Commenting JavaScript Code Commenting your code is very important // comment rest of line Or /* comment block with many lines */ csci 20218

XP Using Comments to Hide JavaScript Code <!--Hide from nonJavaScript browsers JavaScript commands // Stop hiding from older browsers --> csci 20219

XP Debugging Your JavaScript Programs Debugging is the process of searching code to locate a source of trouble There are three types of errors: – Load-time errors – Run-time errors – Logical errors csci 20220

XP Debugging Your JavaScript Programs Microsoft: Microsoft Script Debugger Firefox: Firefox Error Console Modular code entails breaking up a program’s different tasks into small, manageable chunks An alert dialog box can be generated to display a text message with an OK button alert(text); csci 20221