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Programming with JavaScript (Chapter 10)

Programming with JavaScript (Chapter 10). Various things. Midterm grades: Friday Winter Career Fair Thursday, April 28, 2011 (11 am to 3 pm). MAC Gym, Wade King Student Rec Center http://www.careers.wwu.edu/careerfair_specialevents.shtml

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Programming with JavaScript (Chapter 10)

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  1. Programming with JavaScript(Chapter 10)

  2. Various things • Midterm grades: Friday • Winter Career Fair • Thursday, April 28, 2011 (11 am to 3 pm). • MAC Gym, Wade King Student Rec Center • http://www.careers.wwu.edu/careerfair_specialevents.shtml • bring resumes, dress in business attire, and research participating employers in advance.

  3. Objectives • The script element • 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 application • Examples of document.write() • Lab4 at http://faculty.wwu.edu/~granier/Spring2011/csci202/labs/lab04/ • LAB 3 ANSWERS csci 202

  4. 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 csci 202

  5. Comparing Java and JavaScript csci 202

  6. 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 202

  7. 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 type="mime-type"> script commands </script> csci 202

  8. 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 202

  9. 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 202

  10. 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: varvariable; varvariable = value; variable = value; where variable is the name of the variable and value is the initial value of the variable. csci 202

  11. 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 202

  12. 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 202

  13. 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 202

  14. 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 202

  15. Creating a JavaScript Function csci 202

  16. 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 202

  17. Accessing an External JavaScript File • The code to access an external script file is: <script src="url" type="mime-type"></script> • Place all script elements that reference external files in the document head csci 202

  18. Commenting JavaScript Code • Commenting your code is very important // comment rest of line • Or /* comment block with many lines*/ csci 202

  19. Using Comments to Hide JavaScript Code <script type="text/javascript"> <!--Hide from nonJavaScript browsers JavaScript commands // Stop hiding from older browsers --> </script> csci 202

  20. 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 202

  21. 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 buttonalert(text); csci 202

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