Javascript Tlabs

JavaScript
JAVASCRIPT IS THE CLIENT SCRIPTING
LANGUAGE OF THE WEB.

What for?
 Simple Addition
 Fun With Text
 Combining Text and Numbers
 Calculation
 Data handling
 Events
 Effects

About
 JavaScript is the world's most popular programming









language.
It is the language for HTML, for the web, for
servers, PCs, laptops, tablets, phones, and more.
A scripting language is a lightweight programming
language.
JavaScript is programming code that can be inserted into
HTML pages.
JavaScript code can be executed by all modern web
browsers.
JavaScript is easy to learn.

Steps to act

1. Inline

2. External

How To
 JavaScripts in HTML must be inserted between
 <script> and </script> tags.
 <script> and </script> tells,
 where the JavaScript starts and ends
 Lines between them
 contain the JavaScript code

What's in it?
 JavaScript is Case Sensitive


Watch your capitalization closely when you write JavaScript
statements

 White Space


JavaScript ignores extra spaces. You can add white space to your
script to make it more readable.


var person="Hege";
var person = "Hege";

 Break up a Code Line


You can break up a code line within a text string with a backslash.
The example below will be displayed properly:
document.write("Hello
World!");
 document.write
("Hello World!");


Comments
 JavaScript Comments
 Comments will not be executed by JavaScript.
 Comments can be added to explain the JavaScript, or to make
the code more readable.
 Single line comments start with //.


// Write to a heading:
document.getElementById("myH1").innerHTML="Welcome to
my Homepage";
// Write to a paragraph:
document.getElementById("myP").innerHTML="This is my first
paragraph.";

 JavaScript Multi-Line Comments
 Multi line comments start with /* and end with */.


/*
The code below will write
to a heading and to a paragraph,
and will represent the start of
my homepage:
*/
document.getElementById("myH1").innerHTML="Welcome to
my Homepage";
document.getElementById("myP").innerHTML="This is my first
paragraph.";

 Using Comments to Prevent Execution
 //document.getElementById("myH1").innerHTML="Welcome
to my Homepage";
document.getElementById("myP").innerHTML="This is my
first paragraph.";
 Using Comments at the End of a Line
 var x=5; // declare x and assign 5 to it
var y=x+2; // declare y and assign x+2 to it

Variables




Your Name
Let's Make a Sentence
Numbers in Variables

 JavaScript variables are "containers" for storing

information


var x=5;
var y=6;
var z=x+y;

 As with algebra,
 JavaScript variables can be used to hold values (x=5) or
expressions (z=x+y).
 Variable can have short names (like x and y) or more

descriptive names


(age, sum, totalvolume).

 Variable names must begin with a letter
 Variable names can also begin with
 $ and _ (but we will not use it)
 Variable names are case sensitive
 (y and Y are different variables)

Data Types
 JavaScript variables can also hold other types of

data, like text values


(person="John Doe").

 In JavaScript a text like "John Doe" is called a string.
 There are many types of JavaScript variables, but for

now, just think of numbers and strings.
 When you assign a text value to a variable, put :


double or single quotes around the value.

 When you assign a numeric value to a variable:
 do not put quotes around the value.

 If you put quotes around a numeric value:
 it will be treated as text.


var pi=3.14;
var person="John Doe";
var answer='Yes I am!';

 Dynamic Types
 var x;
// Now x is undefined
var x = 5;
// Now x is a Number
var x = "John"; // Now x is a String
 Strings
 var answer="It's alright";
var answer="He is called 'Johnny'";
var answer='He is called "Johnny"';

 Numbers
 JavaScript has only one type of numbers. Numbers can be
written with, or without decimals
var x1=34.00; // Written with decimals
var x2=34;
// Written without decimals
 var y=123e5;
// 12300000
var z=123e-5; // 0.00123


 Booleans
 Booleans can only have two values: true or false


var x=true;
var y=false;

Declaring (Creating) Variables
var keyword
 You declare JavaScript variables with the var


var carname;

 After the declaration, the variable is empty
 Assign a value to the variable
 carname="Volvo";
 You can also assign a value to the variable when you

declare it


var carname="Volvo";

Many Variables
 Declare many variables in one statement
 var lastname="Doe", age=30, job="carpenter";
 Declaration can also span multiple lines
 var lastname="Doe",
age=30,
job="carpenter";

Value = undefined
 Variables
 Variable declared without a value will have the value

undefined. are often declared without a value
 The variable carname will have the
value undefined after the execution of the following
statement:


var carname;

 Re-Declaring JavaScript Variables
 var carname="Volvo";
var carname;

Operators

 Arithmetic Operators
 Assignment Operator

Javascript Tlabs

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