Module 1.5.1: Introduction to JavaScript Language

prelim topic

Javascript

• Is a client-side scripting language - it is executed in the client (software) that the viewer is using (browser)

• Each line is processed as it loads in the browser

• Allows us to make interactive webpages

• Is dynamic, event-based, async-friendly, prototype based, object-oriented language

• Is popular because it runs pretty much on very client (iOS, Android, laptops) and on servers (Node.js)

Javascript Statements

• Are codes to be executed by the browser

• Tells the browser what to do

• Commands to the browser

• add semicolons at the end

• can be grouped together into blocks using curly brackets

• try…catch statement allows to test a block of code for errors

//

• is the javascript single-line comment

/* */

• Is the javascript multi-line comment

Javascript variables

• are containers for storing information (ex: x=15; length=60.10;)

• hold values or expressions

• can hold a text value in name='“multimedia”

• var statement can declare javascript variables: var x; var name;

• They are case sensitive

Variable names

Arithmetic Operators

• These perform arithmetic operations between values of the variables

• Ex: Addition (+), Subtraction (-), Multiplication (*), Division (/), Modulus (%), Increment (+ +), Decrement (- -)

Assignment Operators

• These assign values to variables

• Ex: =, +, - =, * =, / =, % =

Comparison Operators

• These determine equality or different between variables or values

• Ex: Equal to (= =), Exactly equal to (= = =), Not equal (! =), Greater than (>), Less than (<), Greater than or equal to (>=), Lesser than or equal to (<=)

Logical Operators

• These impose the logic between variables or values

• Ex: AND (&&), OR (| |), NOT (!)

Conditional Operators

• These assign value to variable based on some conditions

• ?:

if statement

• to execute some code only if specified condition is true

if…else statement

• to execute some code if the condition is true and another code if the condition is false

if…else if…else statement

• To select one of many blocks of code to be executed

switch statement

• To select one of many blocks of code to be executed

Javascript Looping

• It executes the same block of codes

• executes a specified number of times

• execution can be controlled by some control logic

• Ex: for, while, do…while statements

• Ex: for…in to iterate through the elements of an array

Break

• This breaks the loop and follows the code after the loop

Continue

• This breaks the loop and continues with the next value

Javascript Functions

• These can be called with the function name

• Can also be executed by an event

• Can have parameters and return statement

Javascript Events

• These are actions that can be detected (Ex: OnMouseOver, onMouseOut)

• Are normally associated with functions

• Ex:
  <input type=”text” size=”30” id=”email” onChange=”checkEmail()”>

Alert Box

• This is a javascript popup box to make sure information comes through the user

Confirm Box

• This is a javascript popup box to verify or accept something

Prompt Box

• This is a javascript popup box for the user to input a value before entering a page