Exploring Java Script - Introduction to Java Script - Lecture Slides, Slides of Javascript programming

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Exploring JavaScript

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disabled JavaScript.

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Low-Level Print

• When in doubt, you can always add an to your JavaScript

• The alert() function takes a string as a parameter and pauses the

JavaScript execution until you press "OK"

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Including JavaScript

• Three Patterns

• As part of an event (i.e. onclick) in an HTML tag

• Inline within the document

• From a file

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Click Me

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JavaScript on a tag

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JavaScript inline that

will pass validation

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script.js: document.write("

Hello World

");

JavaScript in a

separate file

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Syntax Errors

• Like any language, we can make syntax errors

• By default, browsers silently eat any kind of JavaScript error

• But the code stops running in that file or script section

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Seeing the Error

• Since the end-user really cannot take any action to fix the

JavaScript coming as part of a web page, the browser eats the errors.

• As a developer, we need to look for the errors - sometimes it takes

a minute to even remember to check for a JS error

Console Logging

• Debugging using alert() can get tiring - sometimes you want to

record what happens in case something goes wrong

• http://getfirebug.com/logging

• console.log("String") - and many more functions

• Note: Requires recent browsers

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Console is Not Always There

• Some browsers only define the console if a debugger is

running window.console && console.log(...) if (typeof console == "undefined") { this.console = {log: function() {} } http://stackoverflow.com/questions/3326650/console-is-undefined-error-for-internet- explorer

Using the Debugger

• Add the FireBug FireFox Extension

• Enable FireBug, reload

• Set Breakpoint, and reload again

JavaScript Language

Comments in JavaScript =

Awesome

// This is a comment /* This is a section of multiline comments that will not be interpreted */

Statements

• White space and newlines do not matter

• Statements end with semicolon ;

• There are cases where you can the semicolon off - but don't

bother exploiting the feature - just add semicolons like C, Java, PHP, C++, etc..

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Variable Names

• Valid Characters: a-z, A-Z, 0-9, _ and $

• Must not start with a number

• Names are case sensitive

• Starting with a dollar sign is considered "tacky"