1. What is JavaScript?
- JavaScript was designed to add interactivity to HTML pages
- JavaScript is a scripting language - a scripting language is a lightweight programming language
- A JavaScript is lines of executable computer code
- A JavaScript is usually embedded directly in HTML pages
- JavaScript is an interpreted language (means that scripts execute without preliminary compilation)
- Everyone can use JavaScript without purchasing a license
- JavaScript is supported by all major browsers, like Netscape and Internet Explorer
2. How to Put a JavaScript Into an HTML Page
<html><body><script type="text/javascript">document.write("Hello World!")</script></body></html>The code above will produce this output on an HTML page:Hello World!
3. Where to Put the JavaScript?
Scripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, other times when a user triggers an event.
Scripts in the head section: Scripts to be executed when they are called, or when an event is triggered, go in the head section. When you place a script in the head section, you will ensure that the script is loaded before anyone uses it.
<html><head><script type="text/javascript"> some statements</script></head> Scripts in the body section:
Scripts to be executed when the page loads go in the body section. When you place a script in the body section it generates the content of the page.
<html><head></head><body><script type="text/javascript">some statements
</script></body>Scripts in both the body and the head section: You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section.
<html><head><script type="text/javascript">some statements
</script></head><body><script type="text/javascript">some statements
</script></body>4. Define Variables
A variable is a "container" for information you want to store. A variable's value can change during the script. You can refer to a variable by name to see its value or to change its value.Rules for Variable names:
- Variable names are case sensitive
- They must begin with a letter or the underscore character
5. How to declare a Variable?
You can create a variable with the var statement:var strname = some value
You can also create a variable without the var statement:
strname = some value
6. How to Assign a Value to a Variable?
You assign a value to a variable like this:var strname = "Hege"
Or like this:
strname = "Hege"
The variable name is on the left side of the expression and the value you want to assign to the variable is on the right. Now the variable "strname" has the value "Hege".
7. Explain Arithmetic Operators
| Operator | Description | Example | Result |
| + | Addition | x=2 x+2 | 4 |
| - | Subtraction | x=2 5-x | 3 |
| * | Multiplication | x=4 x*5 | 20 |
| / | Division | 15/5 5/2 | 3 2.5 |
| % | Modulus (division remainder) | 5%2 10%8 10%2 | 1 2 0 |
| ++ | Increment | x=5 x++ | x=6 |
| -- | Decrement | x=5 x-- | X=4 |
8. What are the Assignment Operators available in Javascript?
| Operator | Example | Is The Same As |
| = | x=y | x=y |
| += | x+=y | x=x+y |
| -= | x-=y | x=x-y |
| *= | x*=y | x=x*y |
| /= | x/=y | x=x/y |
| %= | x%=y | x=x%y |
9. Comparison Operators in Javascript.
| Operator | Description | Example |
| == | is equal to | 5==8 returns false |
| != | is not equal | 5!=8 returns true |
| > | is greater than | 5>8 returns false |
| < | is less than | 5<8 returns true |
| >= | is greater than or equal to | 5>=8 returns false |
| <= | is less than or equal to | 5<=8 returns true |
10. Logical Operators in javascript.
| Operator | Description | Example |
| && | and | x=6 (x < 10 && y > 1) returns truey=3 |
| || | or | x=6 (x==5 || y==5) returns falsey=3 |
| ! | not | x=6 !(x==y) returns truey=3 |
11. String Operator in Javascript.
A string is most often text, for example "Hello World!". To stick two or more string variables together, use the + operator.txt1="What a very"txt2="nice day!"txt3=txt1+txt2 |
To add a space between two string variables, insert a space into the expression, OR in one of the strings.
txt1="What a very"txt2="nice day!"txt3=txt1+" "+txt2ortxt1="What a very "txt2="nice day!"txt3=txt1+txt2 |
12. What is Functions?
A function contains some code that will be executed by an event or a call to that function. A function is a set of statements. You can reuse functions within the same script, or in other documents. You define functions at the beginning of a file (in the head section), and call them later in the document. It is now time to take a lesson about the alert-box:
This is JavaScript's method to alert the user.Alert("This is a message") |
13. How to Define a Function
To create a function you define its name, any values ("arguments"), and some statements:function myfunction(argument1,argument2,etc){some statements} |
A function with no arguments must include the parentheses:
function myfunction(){some statements} |
By placing functions in the head section of the document, you make sure that all the code in the function has been loaded before the function is called.
Some functions return a value to the calling expression
function result(a,b){c=a+breturn c} |
14. How to Call a Function?
A function is not executed before it is called.You can call a function containing arguments:
myfunction(argument1,argument2,etc) |
myfunction() |
The return Statement
Functions that will return a result must use the "return" statement. This statement specifies the value which will be returned to where the function was called from. Say you have a function that returns the sum of two numbers: function total(a,b){result=a+breturn result} |
sum=total(2,3) |
15. What is DHTML?
DHTML stands for Dynamic HTML. When implemented in full it allows complete control of all the structures and contents of a Web page by exposing every part of the Document Object Model (DOM) to control by JavaScript. Thus the position, visibility, color, size, content, etc of every aspect of a web page can be dynamically controlled.
- Positioning: precisely placing blocks of content on the page and, if desired, moving these blocks around (strictly speaking, a subset of style modifications).
- Style modifications: on-the-fly altering the aesthetics of content on the page.
- Event handling: how to relate user events to changes in positioning or other style modifications.
17. Write short notes on layers.
In general, "layer" refers to elements that can be positioned at exact coordinates on the page. These elements can be defined with the DIV, SPAN, LAYER, or ILAYER tags. Layers created with DIV and SPAN are referred to as CSS layers because their properties are defined by the Cascading Style Sheets specification by the World Wide web Consortium. This specification defines style properties (e.g. font, color, padding, margin, word-spacing) in addition to the positioning properties associated with layers (top, left, z-index, visibility).
18. How DHTML Does it Work?
Various elements of a web page such as images and blocks of text are organized into groups with the <div> or <layer> tags. The groups are then given a list of properties using the cascading style sheet specification and a name to distinguish them from each other. Then through the use of a scripting language, you can dynamically change the CSS attribute of each group. It's really quite neat how the three elements of web design can come together in a dynamic union.
DHTML gives you ability to position elements of a web page to precise (x,y,z) coordinates and dynamically change the position with script. Every property of a web page element can be altered with the use of a script language. Some properties include color, size, visibility, alignment, etc.. You can achieve some awesome effects with DHTML.
20. Write About The Technology Components Of DHTML.
The major components of Dynamic HTML technology are:-
- Style Sheets (NS) (MS) let you specify the stylistic attributes of the typographic elements of your web page. They let you change the color, size, or style of the text on a page without waiting for the screen to refresh.
- Content Positioning (NS) (MS) lets a web developer animate any element on a web page, moving pictures, text, and objects at will. It lets you ensure that pieces of content are displayed on the page exactly where you want them to appear, and you can modify their appearance and location after the page has been displayed.
- Dynamic Content (MS) actually changes the words, pictures, or multimedia on a page without another trip to the web Server.
- Data Binding (MS) lets you get all the information you need to ask questions, change elements, and get results without going back to the web server.
- Downloadable Fonts (NS) let you use the fonts of your choice to enhance the appearance of your text. Then you can package the fonts with the page so that the text is always displayed with your chosen fonts.
Introduction to JavaScript
JavaScript is used in millions of Web pages to improve the design, validate forms, detect browsers, create cookies, and much more.
JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Mozilla, Firefox, Netscape, Opera.
What is JavaScript?
- JavaScript was designed to add interactivity to HTML pages
- JavaScript is a scripting language (a scripting language is a lightweight programming language)
- A JavaScript consists of lines of executable computer code
- A JavaScript is usually embedded directly into HTML pages
- JavaScript is an interpreted language (means that scripts execute without preliminary compilation)
- Everyone can use JavaScript without purchasing a license
Are Java and JavaScript the Same?
NO!Java and JavaScript are two completely different languages in both concept and design!
Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.
What can a JavaScript Do?
- JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
- JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page
- JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
- JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
- JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server, this will save the server from extra processing
- JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
- JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer
How to Put a JavaScript Into an HTML Page
<html><body><script type="text/javascript">document.write("Hello World!")</script></body></html> |
| Hello World! |
Example Explained
To insert a JavaScript into an HTML page, we use the <script> tag (also use the type attribute to define the scripting language).So, the <script type="text/javascript"> and </script> tells where the JavaScript starts and ends:
<html><body><script type="text/javascript">...</script></body></html> |
By entering the document.write command between the <script type="text/javascript"> and </script> tags, the browser will recognize it as a JavaScript command and execute the code line. In this case the browser will write Hello World! to the page:
<html><body><script type="text/javascript">document.write("Hello World!")</script></body></html> |
Ending Statements With a Semicolon?
With traditional programming languages, like C++ and Java, each code statement has to end with a semicolon.Many programmers continue this habit when writing JavaScript, but in general, semicolons are optional! However, semicolons are required if you want to put more than one statement on a single line.
How to Handle Older Browsers
Browsers that do not support JavaScript will display the script as page content. To prevent them from doing this, we may use the HTML comment tag:<script type="text/javascript"><!--document.write("Hello World!")//--></script> |
Where to Put the JavaScript
JavaScripts in the body section will be executed WHILE the page loads.
JavaScripts in the head section will be executed when CALLED.
JavaScripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, other times when a user triggers an event.Scripts in the head section: Scripts to be executed when they are called, or when an event is triggered, go in the head section. When you place a script in the head section, you will ensure that the script is loaded before anyone uses it.
<html><head><script type="text/javascript">....</script></head> |
<html><head></head><body><script type="text/javascript">....</script></body> |
<html><head><script type="text/javascript">....</script></head><body><script type="text/javascript">....</script></body> |
Using an External JavaScript
Sometimes you might want to run the same JavaScript on several pages, without having to write the same script on every page.To simplify this, you can write a JavaScript in an external file. Save the external JavaScript file with a .js file extension.
Note: The external script cannot contain the <script> tag!
To use the external script, point to the .js file in the "src" attribute of the <script> tag:
<html><head><script src="xxx.js"></script></head><body></body></html> |
Variables
A variable is a "container" for information you want to store. A variable's value can change during the script. You can refer to a variable by name to see its value or to change its value.Rules for variable names:
- Variable names are case sensitive
- They must begin with a letter or the underscore character
Declare a Variable
You can create a variable with the var statement:var strname = some value |
strname = some value |
Assign a Value to a Variable
You can assign a value to a variable like this:var strname = "Hege" |
strname = "Hege" |
Lifetime of Variables
When you declare a variable within a function, the variable can only be accessed within that function. When you exit the function, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different functions, because each is recognized only by the function in which it is declared.If you declare a variable outside a function, all the functions on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.
JavaScript If...Else Statements
Conditional statements in JavaScript are used to perform different actions based on different conditions.
Conditional Statements
Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.In JavaScript we have the following conditional statements:
- if statement - use this statement if you want to execute some code only if a specified condition is true
- if...else statement - use this statement if you want to execute some code if the condition is true and another code if the condition is false
- if...else if....else statement - use this statement if you want to select one of many blocks of code to be executed
- switch statement - use this statement if you want to select one of many blocks of code to be executed
If Statement
You should use the if statement if you want to execute some code only if a specified condition is true.Syntax
if (condition){code to be executed if condition is true} |
Example 1
<script type="text/javascript">//Write a "Good morning" greeting if//the time is less than 10var d=new Date()var time=d.getHours() if (time<10) {document.write("<b>Good morning</b>")}</script> |
Example 2
<script type="text/javascript">//Write "Lunch-time!" if the time is 11var d=new Date()var time=d.getHours() if (time==11) {document.write("<b>Lunch-time!</b>")}</script> |
Notice that there is no ..else.. in this syntax. You just tell the code to execute some code only if the specified condition is true.
If...else Statement
If you want to execute some code if a condition is true and another code if the condition is not true, use the if....else statement.Syntax
if (condition){code to be executed if condition is true}else{code to be executed if condition is not true} |
Example
<script type="text/javascript">//If the time is less than 10,//you will get a "Good morning" greeting.//Otherwise you will get a "Good day" greeting.var d = new Date()var time = d.getHours() if (time < 10) {document.write("Good morning!")}else{document.write("Good day!")}</script> |
If...else if...else Statement
You should use the if....else if...else statement if you want to select one of many sets of lines to execute.Syntax
if (condition1){code to be executed if condition1 is true}else if (condition2){code to be executed if condition2 is true}else{code to be executed if condition1 andcondition2 are not true} |
Example
<script type="text/javascript">var d = new Date()var time = d.getHours()if (time<10){document.write("<b>Good morning</b>")}else if (time>10 && time<16){document.write("<b>Good day</b>")}else{document.write("<b>Hello World!</b>")}</script> |
Conditional statements in JavaScript are used to perform different actions based on different conditions.
The JavaScript Switch Statement
You should use the switch statement if you want to select one of many blocks of code to be executed.Syntax
switch(n){case 1: execute code block 1 break case 2: execute code block 2 breakdefault: code to be executed if n is different from case 1 and 2} |
Example
<script type="text/javascript">//You will receive a different greeting based//on what day it is. Note that Sunday=0,//Monday=1, Tuesday=2, etc.var d=new Date()theDay=d.getDay()switch (theDay){case 5: document.write("Finally Friday") breakcase 6: document.write("Super Saturday") breakcase 0: document.write("Sleepy Sunday") breakdefault: document.write("I'm looking forward to this weekend!")}</script> |
JavaScript Operators
Arithmetic Operators
| Operator | Description | Example | Result |
| + | Addition | x=2 y=2 x+y | 4 |
| - | Subtraction | x=5 y=2 x-y | 3 |
| * | Multiplication | x=5 y=4 x*y | 20 |
| / | Division | 15/5 5/2 | 3 2.5 |
| % | Modulus (division remainder) | 5%2 10%8 10%2 | 1 2 0 |
| ++ | Increment | x=5 x++ | x=6 |
| -- | Decrement | x=5 x-- | x=4 |
Assignment Operators
| Operator | Example | Is The Same As |
| = | x=y | x=y |
| += | x+=y | x=x+y |
| -= | x-=y | x=x-y |
| *= | x*=y | x=x*y |
| /= | x/=y | x=x/y |
| %= | x%=y | x=x%y |
Comparison Operators
| Operator | Description | Example |
| == | is equal to | 5==8 returns false |
| === | is equal to (checks for both value and type) | x=5 x==y returns truey="5" x===y returns false |
| != | is not equal | 5!=8 returns true |
| > | is greater than | 5>8 returns false |
| < | is less than | 5<8 returns true |
| >= | is greater than or equal to | 5>=8 returns false |
| <= | is less than or equal to | 5<=8 returns true |
Logical Operators
| Operator | Description | Example |
| && | and | x=6 (x < 10 && y > 1) returns truey=3 |
| || | or | x=6 (x==5 || y==5) returns falsey=3 |
| ! | not | x=6 !(x==y) returns truey=3 |
String Operator
A string is most often text, for example "Hello World!". To stick two or more string variables together, use the + operator.txt1="What a very"txt2="nice day!"txt3=txt1+txt2 |
To add a space between two string variables, insert a space into the expression, OR in one of the strings.
txt1="What a very"txt2="nice day!"txt3=txt1+" "+txt2ortxt1="What a very "txt2="nice day!"txt3=txt1+txt2 |
Conditional Operator
JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.Syntax
variablename=(condition)?value1:value2 |
Example
greeting=(visitor=="PRES")?"Dear President ":"Dear " |
JavaScript Popup Boxes
In JavaScript we can create three kind of popup boxes: Alert box, Confirm box, and Prompt box.
Alert Box
An alert box is often used if you want to make sure information comes through to the user.When an alert box pops up, the user will have to click "OK" to proceed.
Syntax:
alert("sometext") |
Confirm Box
A confirm box is often used if you want the user to verify or accept something.When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed.
If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false.
Syntax:
confirm("sometext") |
Prompt Box
A prompt box is often used if you want the user to input a value before entering a page.When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering an input value.
If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.
Syntax:
prompt("sometext","defaultvalue") |
JavaScript Functions
A function is a reusable code-block that will be executed by an event, or when the function is called.
JavaScript Functions
To keep the browser from executing a script as soon as the page is loaded, you can write your script as a function.A function contains some code that will be executed only by an event or by a call to that function.
You may call a function from anywhere within the page (or even from other pages if the function is embedded in an external .js file).
Functions are defined at the beginning of a page, in the <head> section.
Example
<html><head><script type="text/javascript">function displaymessage(){alert("Hello World!")}</script></head><body><form><input type="button" value="Click me!"onclick="displaymessage()" ></form></body></html> |
If the line: alert("Hello world!!"), in the example above had not been written within a function, it would have been executed as soon as the line was loaded. Now, the script is not executed before the user hits the button. We have added an onClick event to the button that will execute the function displaymessage() when the button is clicked.
How to Define a Function
The syntax for creating a function is:function functionname(var1,var2,...,varX){some code} |
Note: A function with no parameters must include the parentheses () after the function name:
function functionname(){some code} |
The return Statement
The return statement is used to specify the value that is returned from the function.So, functions that are going to return a value must use the return statement.
Example
The function below should return the product of two numbers (a and b):function prod(a,b){x=a*breturn x} |
product=prod(2,3) |
JavaScript For Loop
Loops in JavaScript are used to execute the same block of code a specified number of times or while a specified condition is true.
JavaScript Loops
Very often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal lines in a script we can use loops to perform a task like this.In JavaScript there are two different kind of loops:
- for - loops through a block of code a specified number of times
- while - loops through a block of code while a specified condition is true
The for Loop
The for loop is used when you know in advance how many times the script should run.Syntax
for (var=startvalue;var<=endvalue;var=var+increment) { code to be executed} |
Explanation: The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10. i will increase by 1 each time the loop runs.
Note: The increment parameter could also be negative, and the <= could be any comparing statement.
<html><body><script type="text/javascript">var i=0for (i=0;i<=10;i++){document.write("The number is " + i)document.write("<br />")}</script></body></html> |
The number is 0The number is 1The number is 2The number is 3The number is 4The number is 5The number is 6The number is 7The number is 8The number is 9The number is 10 |
JavaScript While Loop
Loops in JavaScript are used to execute the same block of code a specified number of times or while a specified condition is true.
The while loop
The while loop is used when you want the loop to execute and continue executing while the specified condition is true.while (var<=endvalue){ code to be executed} |
Example
Explanation: The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10. i will increase by 1 each time the loop runs.
<html><body><script type="text/javascript">var i=0while (i<=10){document.write("The number is " + i)document.write("<br />")i=i+1}</script></body></html> |
The number is 0The number is 1The number is 2The number is 3The number is 4The number is 5The number is 6The number is 7The number is 8The number is 9The number is 10 |
The do...while Loop
The do...while loop is a variant of the while loop. This loop will always execute a block of code ONCE, and then it will repeat the loop as long as the specified condition is true. This loop will always be executed once, even if the condition is false, because the code is executed before the condition is tested.do{ code to be executed}while (var<=endvalue) |
<html><body><script type="text/javascript">var i=0do {document.write("The number is " + i)document.write("<br />")i=i+1}while (i<0)</script></body></html> |
The number is 0 |
JavaScript Break and Continue
JavaScript break and continue Statements
There are two special statements that can be used inside loops: break and continue.Break
The break command will break the loop and continue executing the code that follows after the loop (if any).Example
<html><body><script type="text/javascript">var i=0for (i=0;i<=10;i++){if (i==3){break}document.write("The number is " + i)document.write("<br />")}</script></body></html> |
The number is 0The number is 1The number is 2 |
Continue
The continue command will break the current loop and continue with the next value.Example
<html><body><script type="text/javascript">var i=0for (i=0;i<=10;i++){if (i==3){continue}document.write("The number is " + i)document.write("<br />")}</script></body></html> |
The number is 0The number is 1The number is 2The number is 4The number is 5The number is 6The number is 7The number is 8The number is 9The number is 10 |
JavaScript For...In Statement
The for...in statement is used to loop (iterate) through the elements of an array or through the properties of an object.
JavaScript For...In Statement
The for...in statement is used to loop (iterate) through the elements of an array or through the properties of an object.The code in the body of the for ... in loop is executed once for each element/property.
Syntax
for (variable in object){ code to be executed} |
Example
Using for...in to loop through an array:<html><body><script type="text/javascript">var xvar mycars = new Array()mycars[0] = "Saab"mycars[1] = "Volvo"mycars[2] = "BMW" for (x in mycars){document.write(mycars[x] + "<br />")}</script></body></html> |
JavaScript Events
Events are actions that can be detected by JavaScript.
Events
By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can be detected by JavaScript.Every element on a web page has certain events which can trigger JavaScript functions. For example, we can use the onClick event of a button element to indicate that a function will run when a user clicks on the button. We define the events in the HTML tags.
Examples of events:
- A mouse click
- A web page or an image loading
- Mousing over a hot spot on the web page
- Selecting an input box in an HTML form
- Submitting an HTML form
- A keystroke
Note: Events are normally used in combination with functions, and the function will not be executed before the event occurs!
onload and onUnload
The onload and onUnload events are triggered when the user enters or leaves the page.The onload event is often used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information.
Both the onload and onUnload events are also often used to deal with cookies that should be set when a user enters or leaves a page. For example, you could have a popup asking for the user's name upon his first arrival to your page. The name is then stored in a cookie. Next time the visitor arrives at your page, you could have another popup saying something like: "Welcome John Doe!".
onFocus, onBlur and onChange
The onFocus, onBlur and onChange events are often used in combination with validation of form fields.Below is an example of how to use the onChange event. The checkEmail() function will be called whenever the user changes the content of the field:
<input type="text" size="30"id="email" onchange="checkEmail()">; |
onSubmit
The onSubmit event is used to validate ALL form fields before submitting it.Below is an example of how to use the onSubmit event. The checkForm() function will be called when the user clicks the submit button in the form. If the field values are not accepted, the submit should be cancelled. The function checkForm() returns either true or false. If it returns true the form will be submitted, otherwise the submit will be cancelled:
<form method="post" action="xxx.htm"onsubmit="return checkForm()"> |
onMouseOver and onMouseOut
onMouseOver and onMouseOut are often used to create "animated" buttons.Below is an example of an onMouseOver event. An alert box appears when an onMouseOver event is detected:
<a href="http://www.w3schools.com"onmouseover="alert('An onMouseOver event');return false"><img src="sch.gif" width="100" height="30"></a> |
JavaScript Special Characters
In JavaScript you can add special characters to a text string by using the backslash sign.
Insert Special Characters
The backslash (\) is used to insert apostrophes, new lines, quotes, and other special characters into a text string.Look at the following JavaScript code:
var txt="We are the so-called "Vikings" from the north."document.write(txt) |
To solve this problem, you must place a backslash (\) before each double quote in "Viking". This turns each double quote into a string literal:
var txt="We are the so-called \"Vikings\" from the north."document.write(txt) |
Here is another example:
document.write ("You \& me are singing!") |
You & me are singing! |
| Code | Outputs |
| \' | single quote |
| \" | double quote |
| \& | ampersand |
| \\ | backslash |
| \n | new line |
| \r | carriage return |
| \t | tab |
| \b | backspace |
| \f | form feed |
JavaScript Guidelines
Some other important things to know when scripting with JavaScript.
JavaScript is Case Sensitive
A function named "myfunction" is not the same as "myFunction" and a variable named "myVar" is not the same as "myvar".JavaScript is case sensitive - therefore watch your capitalization closely when you create or call variables, objects and functions.
White Space
JavaScript ignores extra spaces. You can add white space to your script to make it more readable. The following lines are equivalent:name="Hege"name = "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
You can add comments to your script by using two slashes //://this is a commentdocument.write("Hello World!") |
/* This is a commentblock. It containsseveral lines */document.write("Hello World!") |
JavaScript Objects Introduction
JavaScript is an Object Oriented Programming (OOP) language.
An OOP language allows you to define your own objects and make your own variable types.
Object Oriented Programming
JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you to define your own objects and make your own variable types.However, creating your own objects will be explained later, in the Advanced JavaScript section. We will start by looking at the built-in JavaScript objects, and how they are used. The next pages will explain each built-in JavaScript object in detail.
Note that an object is just a special kind of data. An object has properties and methods.
Properties
Properties are the values associated with an object.In the following example we are using the length property of the String object to return the number of characters in a string:
<script type="text/javascript">var txt="Hello World!"document.write(txt.length)</script> |
12 |
Methods
Methods are the actions that can be performed on objects.In the following example we are using the toUpperCase() method of the String object to display a text in uppercase letters:
<script type="text/javascript">var str="Hello world!"document.write(str.toUpperCase())</script> |
HELLO WORLD! |
JavaScript String Object
The String object is used to manipulate a stored piece of text.
String object
The String object is used to manipulate a stored piece of text.Examples of use:
The following example uses the length property of the String object to find the length of a string:
var txt="Hello world!"document.write(txt.length) |
12 |
var txt="Hello world!"document.write(txt.toUpperCase()) |
HELLO WORLD! |
Complete String Object Reference
For a complete reference of all the properties and methods that can be used with the String object, go to our complete String object reference.The reference contains a brief description and examples of use for each property and method!
JavaScript Date Object
The Date object is used to work with dates and times.
Defining Dates
The Date object is used to work with dates and times.We define a Date object with the new keyword. The following code line defines a Date object called myDate:
var myDate=new Date() |
Manipulate Dates
We can easily manipulate the date by using the methods available for the Date object.In the example below we set a Date object to a specific date (14th January 2010):
var myDate=new Date()myDate.setFullYear(2010,0,14) |
var myDate=new Date()myDate.setDate(myDate.getDate()+5) |
Comparing Dates
The Date object is also used to compare two dates.The following example compares today's date with the 14th January 2010:
var myDate=new Date()myDate.setFullYear(2010,0,14)var today = new Date()if (myDate>today) alert("Today is before 14th January 2010")else alert("Today is after 14th January 2010") |
Complete Date Object Reference
For a complete reference of all the properties and methods that can be used with the Date object, go to our complete Date object reference.The reference contains a brief description and examples of use for each property and method!
JavaScript Array Object
The Array object is used to store a set of values in a single variable name.
Defining Arrays
The Array object is used to store a set of values in a single variable name.We define an Array object with the new keyword. The following code line defines an Array object called myArray:
var myArray=new Array() |
1:
var mycars=new Array()mycars[0]="Saab"mycars[1]="Volvo"mycars[2]="BMW" |
var mycars=new Array(3)mycars[0]="Saab"mycars[1]="Volvo"mycars[2]="BMW" |
var mycars=new Array("Saab","Volvo","BMW") |
Accessing Arrays
You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0.The following code line:
document.write(mycars[0]) |
Saab |
Modify Values in Existing Arrays
To modify a value in an existing array, just add a new value to the array with a specified index number:mycars[0]="Opel" |
document.write(mycars[0]) |
Opel |
Complete Array Object Reference
For a complete reference of all the properties and methods that can be used with the Array object, go to our complete Array object reference.The reference contains a brief description and examples of use for each property and method!
JavaScript Boolean Object
The Boolean object is used to convert a non-Boolean value to a Boolean value (true or false).
Boolean Object
The Boolean object is an object wrapper for a Boolean value.The Boolean object is used to convert a non-Boolean value to a Boolean value (true or false).
We define a Boolean object with the new keyword. The following code line defines a Boolean object called myBoolean:
var myBoolean=new Boolean() |
All the following lines of code create Boolean objects with an initial value of false:
var myBoolean=new Boolean()var myBoolean=new Boolean(0)var myBoolean=new Boolean(null)var myBoolean=new Boolean("")var myBoolean=new Boolean(false)var myBoolean=new Boolean(NaN) |
var myBoolean=new Boolean(true)var myBoolean=new Boolean("true")var myBoolean=new Boolean("false")var myBoolean=new Boolean("Richard") |
Complete Boolean Object Reference
For a complete reference of all the properties and methods that can be used with the Boolean object, go to our complete Boolean object reference.The reference contains a brief description and examples of use for each property and method!
JavaScript Math Object
The Math object allows you to perform common mathematical tasks.
Math Object
The Math object allows you to perform common mathematical tasks.The Math object includes several mathematical values and functions. You do not need to define the Math object before using it.
Mathematical Values
JavaScript provides eight mathematical values (constants) that can be accessed from the Math object. These are: E, PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log of E.You may reference these values from your JavaScript like this:
Math.EMath.PIMath.SQRT2Math.SQRT1_2Math.LN2Math.LN10Math.LOG2EMath.LOG10E |
Mathematical Methods
In addition to the mathematical values that can be accessed from the Math object there are also several functions (methods) available.Examples of functions (methods):
The following example uses the round() method of the Math object to round a number to the nearest integer:
document.write(Math.round(4.7)) |
5 |
document.write(Math.random()) |
0.8669997601016495 |
document.write(Math.floor(Math.random()*11)) |
3 |
Complete Math Object Reference
For a complete reference of all the properties and methods that can be used with the Math object, go to our complete Math object reference.The reference contains a brief description and examples of use for each property and method!
The Navigator Object
The JavaScript Navigator object contains all information about the visitor's browser. We are going to look at two properties of the Navigator object:- appName - holds the name of the browser
- appVersion - holds, among other things, the version of the browser
Example
<html><body><script>with(navigator){ document.writeln("Browser Code Name:"+appCodeName+"<br>") document.writeln("Browser Name:"+appName+"<br>") document.writeln("Browser Version:"+appVersion+"<br>") document.writeln("Language:"+language+"<br>") document.writeln("Operating Platform:"+platform+"<br>") document.writeln("User Agent:"+userAgent)}</script></body></html> |
<html><body><script>with(navigator){ document.writeln("Browser Code Name:"+appCodeName+"<br>") document.writeln("Browser Name:"+appName+"<br>") document.writeln("Browser Version:"+appVersion+"<br>") document.writeln("Language:"+language+"<br>") document.writeln("Operating Platform:"+platform+"<br>") document.writeln("User Agent:"+userAgent)}</script></body></html>The variable browser in the example above holds the name of the browser, i.e. "Netscape" or "Microsoft Internet Explorer".
The appVersion property in the example above returns a string that contains much more information than just the version number, but for now we are only interested in the version number. To pull the version number out of the string we are using a function called parseFloat(), which pulls the first thing that looks like a decimal number out of a string and returns it.
IMPORTANT! The version number is WRONG in IE 5.0 or later! Microsoft start the appVersion string with the numbers 4.0. in IE 5.0 and IE 6.0!!! Why did they do that??? However, JavaScript is the same in IE6, IE5 and IE4, so for most scripts it is ok.
Example
The script below displays a different alert, depending on the visitor's browser:<html><head><script type="text/javascript">function detectBrowser()
{
var browser=navigator.appNamevar b_version=navigator.appVersionvar version=parseFloat(b_version)if ((browser=="Netscape"||browser=="Microsoft Internet Explorer")&& (version>=4))
{alert("Your browser is good enough!")}else {alert("It's time to upgrade your browser!")}
}</script></head><body onload="detectBrowser()"></body></html> |
JavaScript Timing Events
With JavaScript, it is possible to execute some code NOT immediately after a function is called, but after a specified time interval. This is called timing events.
JavaScript Timing Events
With JavaScript, it is possible to execute some code NOT immediately after a function is called, but after a specified time interval. This is called timing events.It's very easy to time events in JavaScript. The two key methods that are used are:
- setTimeout() - executes a code some time in the future
- clearTimeout() - cancels the setTimeout()
setTimeout()
Syntax
var t=setTimeout("javascript statement",milliseconds) |
The first parameter of setTimeout() is a string that contains a JavaScript statement. This statement could be a statement like "alert('5 seconds!')" or a call to a function, like "alertMsg()".
The second parameter indicates how many milliseconds from now you want to execute the first parameter.
Note: There are 1000 milliseconds in one second.
clearTimeout()
Syntax
clearTimeout(setTimeout_variable) |
Example
When the button is clicked in the example below, an alert box will be displayed after 5 seconds.<html><head><script>var c=setTimeout("alert('Press the OK button to continue')",5000);function clr(){ clearTimeout(c); alert("The setTimeout() method was cancelled");}</script></head><body><form><input type="button" value="OK" onclick="clr()">
</form></html>JavaScript Summary
This tutorial has taught you how to add JavaScript to your HTML pages, to make your web site more dynamic and interactive.You have learned how to create responses to events, validate forms and how to make different scripts run in response to different scenarios.
You have also learned how to create and use objects, and how to use JavaScript's built-in objects.
