Programming Errors and Screen Objects

JavaScript Basics

• JavaScript is a client-side and server-side scripting language that can be inserted into HTML pages and is understood by web browsers.
• It is an Object-based Programming language.

Differences between Java and JavaScript

• Java is a complete programming language, whereas JavaScript is a coded program that can be introduced to HTML pages.
• Java is an object-oriented programming language (OOPS) or structured programming language, similar to C++ or C.
• JavaScript is a client-side scripting language.

JavaScript Data Types

• Number
• String
• Boolean
• Function
• Object
• Undefined

isNaN Function

• The isNaN function returns true if the argument is not a number, otherwise it is false.

JavaScript vs. ASP Script

• JavaScript is a client-side language and does not need the assistance of the web server to execute, making it faster.
• ASP is a server-side language and is always slower than JavaScript.

Negative Infinity

• Negative Infinity is a number in JavaScript that can be derived by dividing a negative number by zero.

Breaking JavaScript Code

• Breaking within a string statement can be done by using a backslash (‘\’) at the end of the first line.
• JavaScript ignores breaks in lines when not within a string statement.

Creator of JavaScript

• Netscape is the software company that developed JavaScript.

Undeclared and Undefined Variables

• Undeclared variables are those that do not exist in a program and are not declared.
• Undefined variables are those that are declared in the program but have not been given any value.

Global Variables

• Global variables are those that are available throughout the length of the code, with no scope.
• The var keyword is used to declare a local variable or object. If the var keyword is omitted, a global variable is declared.

Prompt Box

• A prompt box is a box that allows the user to enter input by providing a text box and a label.

'this' Keyword

• 'this' keyword refers to the object from where it was called.

Timers in JavaScript

• Timers are used to execute a piece of code at a set time or to repeat the code in a given interval of time.
• The functions setTimeout, setInterval, and clearInterval are used to operate timers.

Comments in JavaScript

• // is used for single-line comments.
• /* */ is used for multi-line comments.

ViewState and SessionState

• ViewState is specific to a page in a session.
• SessionState is specific to user-specific data that can be accessed across all pages in the web application.

=== Operator

• === is called the strict equality operator, which returns true when the two operands are having the same value without any type conversion.

Submitting a Form

• To submit a form using JavaScript, use document.form.submit();

Type Conversion

• JavaScript supports automatic type conversion.

Changing Style/Class of an Element

• The style/class of an element can be changed using document.getElementById(“myText”).style.fontSize = “20”; or document.getElementById(“myText”).className = “anyclass”;.

Reading and Writing a File

• There are two ways to read and write a file using JavaScript: using JavaScript extensions and using a web page and Active X objects.

Looping Structures

• For
• While
• do-while loops

Variable Typing

• Variable typing is used to assign a number to a variable and then assign a string to the same variable.

Converting String to Integer

• The parseInt() function is used to convert numbers between different bases.

== vs. ===

• “==” checks only for equality in value, whereas “===” is a stricter equality test and returns false if either the value or the type of the two variables are different.

Operating System Detection

• The navigator.platform string property is used to detect the operating system on the client machine.

NULL in JavaScript

• The NULL value is used to represent no value or no object.

delete Operator

• The delete keyword is used to delete the property as well as its value.

Undefined Value

• Undefined value means the variable used in the code doesn’t exist, the variable is not assigned to any value, or the property doesn’t exist.

Pop-up Boxes

• There are three types of pop-up boxes available in JavaScript: Alert, Confirm, and Prompt.

Other Topics

• Void(0) is used to prevent the page from refreshing and parameter "zero" is passed while calling.
• Cookies are small text files stored in a computer and are used to store information that websites need.
• The pop() method is used to remove the last element from an array.
• InnerHTML is used to replace the content of an HTML element, but it has some disadvantages.
• Break and continue statements are used to control the flow of loops.
• There are two basic groups of data types in JavaScript: Primitive and Reference types.
• Try… Catch---finally is used to handle exceptions in JavaScript.
• document.write() is used to print the text on the screen.
• blur() function is used to remove the focus from the specified object.
• The ‘Strict’ mode in JavaScript adds certain compulsions to JavaScript and can be enabled by adding the string literal “use strict” above the file.
• The navigator.appVersion string is used to detect the operating system on the client machine.
• Closures are used to retain a variable locally and are used when a function is returned from another function.
• An anonymous function is a function that is declared without any named identifier.
• The difference between .call() and .apply() is in the way arguments are passed to the function.
• Event bubbling is a process in JavaScript that allows DOM elements to be nested inside each other.
• JavaScript is case sensitive.### Hyperlinks and Frames
• The target attribute is used to specify the frame in which a hyperlink should open.

Break and Continue Statements

• The break statement is used to exit the current loop.
• The continue statement is used to continue the current loop with a new iteration.

Web Hosting Systems

• Web-garden and web-farm are both web hosting systems.
• The difference between them is that web-garden uses multiple processors in a single server, while web-farm uses multiple servers.

Object Properties

• Object properties are assigned in the same way as variables.
• Example: Document.form.action = "submit".

File Input/Output in JavaScript

• JavaScript extensions can be used to read and write files.
• Example: fh = fopen(getScriptPath(), 0).

DOM in JavaScript

• DOM stands for Document Object Model.
• It is responsible for how objects in a document interact with each other.
• DOM is required for developing web pages, which includes objects like paragraphs, links, etc.
• It allows for adding or deleting objects, and adding extra capabilities to a web page.

Event Handlers

• An event is an action that results from user activity, such as clicking a link or filling a form.
• An event handler is required to manage the execution of these events.
• Event handlers are an attribute of the object, including the event's name and the action taken if the event occurs.

Deferred Scripts

• By default, HTML parsing is paused until the script has finished executing.
• Deferred scripts delay the execution of the script until the HTML parser is running.
• This reduces the loading time of web pages and makes them display faster.

Functional Components in JavaScript

• First-class functions: Functions can be passed as arguments to other functions, returned as values from other functions, assigned to variables, or stored in data structures.
• Nested functions: Functions defined inside other functions.

Errors in JavaScript

• Load-time errors: Errors that occur at the time of page loading, often due to improper syntax.
• Run-time errors: Errors that occur while the program is running, often due to illegal operations.
• Logic errors: Errors caused by syntactically correct code that does not fulfill the required task.

Screen Objects

• Screen objects are used to read information from the client's screen.
• Properties of screen objects include:
  • AvailHeight: The height of the client's screen.
  • AvailWidth: The width of the client's screen.
  • ColorDepth: The bit depth of images on the client's screen.
  • Height: The total height of the client's screen, including the taskbar.
  • Width: The total width of the client's screen, including the taskbar.

Unshift() Method

• The unshift() method adds elements to the beginning of an array.
• Example: var name = ["john"]; name.unshift("charlie"); name.unshift("joseph", "Jane");.

Escape and Unescape Functions

• The escape() function codes a string for transfer across a network.
• The unescape() function decodes a coded string.

EncodeURI and DecodeURI

• The encodeURI() function converts a URL into its hex coding.
• The decodeURI() function converts the encoded URL back to normal.

InnerHTML

• It is not advised to use innerHTML in JavaScript because it refreshes content every time and is slower.
• There is no scope for validation in innerHTML, making it easier to insert rogue code.

Multidimensional Arrays

• The statement var myArray = [[[]]] declares a three-dimensional array.

JavaScript and ECMA Script

• ECMA Script provides rules and guidelines for JavaScript.
• JavaScript is a scripting language used for web development.

Namespacing

• Namespacing is used to group functions, variables, etc. under a unique name.
• It improves modularity in coding and enables code reuse.

Hiding JavaScript Codes

• To hide JavaScript codes from old browsers that don't support JavaScript, add `