JavaScript is the most popular
scripting language on the internet, and works in all major browsers, such as
Internet Explorer, Firefox, Chrome, Opera, and Safari.
What You Should Already Know
Before you continue you should have a basic understanding of the following:- HTML / XHTML
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
- 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("
" + name + "
") 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 saves 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
JavaScript = ECMAScript
JavaScript is an implementation of the ECMAScript language standard. ECMA-262 is the official JavaScript standard.JavaScript was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all browsers since 1996.
The official standardization was adopted by the ECMA organization (an industry standardization association) in 1997.
The ECMA standard (called ECMAScript-262) was approved as an international ISO (ISO/IEC 16262) standard in 1998.
The development is still in progress..
The HTML
Note: Try to avoid using document.write() in real life JavaScript code. The entire HTML page will be overwritten if document.write() is used inside a function, or after the page is loaded. However, document.write() is an easy way to demonstrate JavaScript output in a tutorial.
Changing HTML Elements
The example below writes the current date into an existing element:Example
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Examples Explained
To insert a JavaScript into an HTML page, use the tells where the JavaScript starts and ends:My First Web Page
This is a paragraph.
... some JavaScript code ... |
In this case the browser will replace the content of the HTML element with id="demo", with the current date:
My First Web Page
This is a paragraph.
document.getElementById("demo").innerHTML=Date(); |
JavaScripts can be put in the and in the
sections of an HTML page.
JavaScript inThe example below writes the current date into an existing element when the page loads:
Note that the JavaScript is placed at the bottom of the page to make sure it is not executed before the element is created. JavaScript Functions and EventsJavaScripts in an HTML page will be executed when the page loads. This is not always what we want.Sometimes we want to execute a JavaScript when an event occurs, such as when a user clicks a button. When this is the case we can put the script inside a function. Events are normally used in combination with functions (like calling a function when an event occurs). You will learn more about JavaScript functions and events in later chapters. JavaScript inThe example below calls a function when a button is clicked:
Scripts in andYou can place an unlimited number of scripts in your document, and you can have scripts in both the body and the head section at the same time.It is a common practice to put all functions in the head section, or at the bottom of the page. This way they are all in one place and do not interfere with page content. Using an External JavaScriptJavaScript can also be placed in external files.External JavaScript files often contain code to be used on several different web pages. External JavaScript files have the file extension .js. Note: External script cannot contain the tags! To use an external script, point to the .js file in the "src" attribute of the Note: Remember to place the script exactly where you normally would write the script!
JavaScript is a sequence of statements to be executed by the
browser.
JavaScript is Case SensitiveUnlike HTML, JavaScript is case sensitive - therefore watch your capitalization closely when you write JavaScript statements, create or call variables, objects and functions.JavaScript StatementsA JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do.This JavaScript statement tells the browser to write "Hello Dolly" to the web page:
The semicolon is optional (according to the JavaScript standard), and the browser is supposed to interpret the end of the line as the end of the statement. Because of this you will often see examples without the semicolon at the end. Note: Using semicolons makes it possible to write multiple statements on one line. JavaScript CodeJavaScript code (or just JavaScript) is a sequence of JavaScript statements.Each statement is executed by the browser in the sequence they are written. This example will write a heading and two paragraphs to a web page:
JavaScript BlocksJavaScript statements can be grouped together in blocks.Blocks start with a left curly bracket {, and end with a right curly bracket }. The purpose of a block is to make the sequence of statements execute together. This example will write a heading and two paragraphs to a web page:
You will learn more about functions and conditions in later chapters.
JavaScript comments can be used
to make the code more readable.
JavaScript CommentsComments can be added to explain the JavaScript, or to make the code more readable.Single line comments start with //. The following example uses single line comments to explain the code:
JavaScript Multi-Line CommentsMulti line comments start with /* and end with */.The following example uses a multi line comment to explain the code:
Using Comments to Prevent ExecutionIn the following example the comment is used to prevent the execution of a single code line (can be suitable for debugging):
Using Comments at the End of a LineIn the following example the comment is placed at the end of a code line:
Variables are
"containers" for storing information.
Do You Remember Algebra From School?Do you remember algebra from school? x=5, y=6, z=x+yDo you remember that a letter (like x) could be used to hold a value (like 5), and that you could use the information above to calculate the value of z to be 11? These letters are called variables, and variables can be used to hold values (x=5) or expressions (z=x+y). JavaScript VariablesAs with algebra, JavaScript variables are used to hold values or expressions.A variable can have a short name, like x, or a more descriptive name, like carname. Rules for JavaScript variable names:
ExampleA variable's value can change during the execution of a script. You can refer to a variable by its name to display or change its value.This example will show you how Declaring (Creating) JavaScript VariablesCreating variables in JavaScript is most often referred to as "declaring" variables.You declare JavaScript variables with the var keyword:
However, you can also assign values to the variables when you declare them:
Note: When you assign a text value to a variable, use quotes around the value. Note: If you redeclare a JavaScript variable, it will not lose its value. Local JavaScript VariablesA variable declared within a JavaScript function becomes LOCAL and can only be accessed within that function. (the variable has local scope).You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared. Local variables are destroyed when you exit the function. You will learn more about functions in a later chapter of this tutorial. Global JavaScript VariablesVariables declared outside a function become GLOBAL, and all scripts and functions on the web page can access it.Global variables are destroyed when you close the page. If you declare a variable, without using "var", the variable always becomes GLOBAL. Assigning Values to Undeclared JavaScript VariablesIf you assign values to variables that have not yet been declared, the variables will automatically be declared as global variables.These statements:
JavaScript ArithmeticAs with algebra, you can do arithmetic operations with JavaScript variables:
= is used to assign values.
+ is used to add values.
The arithmetic operator + is used to add values together.
JavaScript Arithmetic OperatorsArithmetic operators are used to perform arithmetic between variables and/or values.Given that y=5, the table below explains the arithmetic operators:
JavaScript Assignment OperatorsAssignment operators are used to assign values to JavaScript variables.Given that x=10 and y=5, the table below explains the assignment operators:
The + Operator Used on StringsThe + operator can also be used to add string variables or text values together.To add two or more string variables together, use the + operator.
To add a space between the two strings, insert a space into one of the strings:
"What a very nice day" Adding Strings and NumbersThe rule is: If you add a number and a string, the result will be a string!
Comparison operators can be used
in conditional statements to compare Comparison and Logical operators are used
to test for true or false.
Comparison OperatorsComparison operators are used in logical statements to determine equality or difference between variables or values.Given that x=5, the table below explains the comparison operators:
How Can it be Usedvalues and take action depending on the result:
Logical OperatorsLogical operators are used to determine the logic between variables or values.Given that x=6 and y=3, the table below explains the logical operators:
Conditional OperatorJavaScript also contains a conditional operator that assigns a value to a variable based on some condition.Syntax
Example
Conditional statements are used
to perform different actions based on different conditions.
Conditional StatementsVery 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 StatementUse the if statement to execute some code only if a specified condition is true.Syntax
If...else StatementUse the if....else statement to execute some code if a condition is true and another code if the condition is not true.Syntax
If...else if...else StatementUse the if....else if...else statement to select one of several blocks of code to be executed.Syntax
Conditional statements are used
to perform different actions based on different conditions.
The JavaScript Switch StatementUse the switch statement to select one of many blocks of code to be executed.Syntax
JavaScript has three kind of
popup boxes: Alert box, Confirm box, and Prompt box.
Alert BoxAn 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
Confirm BoxA 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
Prompt BoxA 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
Style strings
How to style strings.
The toLowerCase() and toUpperCase() methods
How to convert a string to lowercase or uppercase letters.
The match() method
How to search for a specified value within a string.
Replace characters in a string - replace()
How to replace a specified value with another value in a string.
The indexOf() method
How to return the position of the first found occurrence of a specified value in a string.
The Date object is used to work
with dates and times.
How to use the Date() method to get today's date. getFullYear() Use getFullYear() to get the year. getTime() getTime() returns the number of milliseconds since 01.01.1970. setFullYear() How to use setFullYear() to set a specific date. toUTCString() How to use toUTCString() to convert today's date (according to UTC) to a string. getDay() Use getDay() and an array to write a weekday, and not just a number. Display a clock How to display a clock on your web page. Complete Date Object ReferenceFor 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! Create a Date ObjectThe Date object is used to work with dates and times.Date objects are created with the Date() constructor. There are four ways of instantiating a date:
Once a Date object is created, a number of methods allow you to operate on it. Most methods allow you to get and set the year, month, day, hour, minute, second, and milliseconds of the object, using either local time or UTC (universal, or GMT) time. All dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC) with a day containing 86,400,000 milliseconds. Some examples of instantiating a date:
Set DatesWe 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):
Compare Two DatesThe Date object is also used to compare two dates.The following example compares today's date with the 14th January 2100:
Return today's date and time
How to use the Date() method to get today's date.
var d=new Date(); document.write(d);
getFullYear()
Use getFullYear() to get the year.
var d=new Date(); document.write(d.getFullYear());
getTime()
getTime() returns the number of milliseconds since 01.01.1970 var d=new Date(); document.write(d.getTime() + " milliseconds since 1970/01/01");
setFullYear()
How to use setFullYear() to set a specific date.
var d = new Date(); d.setFullYear(1992,10,3); document.write(d);
toUTCString()
How to use toUTCString() to convert today's date (according to UTC) to a string.
var d=new Date(); document.write("Original form: ");
document.write(d +
" document.write("To string (universal time): "); document.write(d.toUTCString());
getDay()
Use getDay() and an array to write a weekday, and not just a number
var d=new Date(); var weekday=new Array(7); weekday[0]="Sunday"; weekday[1]="Monday"; weekday[2]="Tuesday"; weekday[3]="Wednesday"; weekday[4]="Thursday"; weekday[5]="Friday"; weekday[6]="Saturday";
document.write("Today is " + weekday[d.getDay()]);
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