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JavaScript has 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");

Conditional statements are used to perform different actions based on different conditions.

if statement - use this statement to execute some code only if a specified condition is true

Comparison operators can be used in conditional statements to compare values and take action depending on the result: if (age<18) document.write("Too young");

JavaScript also contains a conditional operator that assigns a value to a variable based on some condition. Syntax variablename=(condition)?value1:value2 

= is used to assign values.

+ is used to add values.

The + operator can also be used to add string variables or text values together.

A function will be executed by an event or by a call to the function.

To keep the browser from executing a script when the page loads, you can put your script into a function.

A function contains code that will be executed by an event or by a call to the function.

Loops execute a block of code a specified number of times, or while a specified condition is true.

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 (variable=startvalue;variable<=endvalue;variable=variable+increment) { code to be executed }

The while Loop The while loop loops through a block of code while a specified condition is true. Syntax while (variable<=endvalue)   {   code to be executed   }

The do...while Loop The do...while loop is a variant of the while loop. This loop will execute the block of code ONCE, and then it will repeat the loop as long as the specified condition is true. Syntax do   {   code to be executed   } while (variable<=endvalue);

The break Statement The break statement will break the loop and continue executing the code that follows after the loop (if any).

<script type="text/javascript"> var i=0; for (i=0;i<=10;i++)   {   if (i==3)     {     break;     }   document.write("The number is " + i);   document.write("<br />");   } </script>

The continue Statement The continue statement will break the current loop and continue with the next value.

JavaScript For...In Statement The for...in statement loops through the elements of an array or through the properties of an object. Syntax for (variable in object)   {   code to be executed   }

The code in the body of the for...in loop is executed once for each element/property.

JavaScript is case sensitive - therefore watch your capitalization closely when you create or call variables, objects and functions.

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.

In JavaScript, a string is started and stopped with either single or double quotes.

The Throw Statement The throw statement allows you to create an exception. If you use this statement together with the try...catch statement, you can control program flow and generate accurate error messages. Syntax throw exception

throw is written in lowercase letters. Using uppercase letters will generate a JavaScript error!

The try...catch statement allows you to test a block of code for errors.

The try...catch Statement The try...catch statement allows you to test a block of code for errors. The try block contains the code to be run, and the catch block contains the code to be executed if an error occurs. Syntax try   {   //Run some code here   } catch(err)   {   //Handle errors here   } Note that try...catch is written in lowercase letters. Using uppercase letters will generate a JavaScript error!

The throw Statement The throw statement can be used together with the try...catch statement, to create an exception for the error

Events are actions that can be detected by JavaScript.

Every element on a web page has certain events which can trigger a JavaScript. 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 field in an HTML form Submitting an HTML form A keystroke

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