Exceptions In JavaScript

pradeep's Avatar author of Exceptions In JavaScript
This is an article on Exceptions In JavaScript in JavaScript and AJAX.

Introduction



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.

Use the throw statement to throw an exception. When you throw an exception, expression specifies the value of the exception. Each of the following throws an exception:

Code: JavaScript
throw "Error2"; // generates an exception with a string value
    throw 42; // generates an exception with the value 42
    throw true; // generates an exception with the value true
 

Syntax



throw(exception)

The exception can be a string, integer, Boolean or an object.

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

Example



Code: JavaScript
function userException(msg,errCode)
    {
        this.description = msg;
        this.err = errCode;
    }
   
    function divide(operand,divisor)
    {
        if(divisor==0)
        {
            var ex = new userException('Division by zero is not possible');
            throw ex;
        }
   
        return operand/divisor;
    }
   
    try
    {
        var result = divide(123,0); // trying to divide by zero
    }
    catch(err)
    {
        alert('Exception: '+err.description+' ('+err.err+')');
    }
kush_2207's Avatar, Join Date: Jun 2007
Go4Expert Member
Theres also another keyword "throws" which many times novice java geeks get confused with.
"throws" clause allows any method to throw exception to the caller. In the sense when it is used with any method, that method will not catch the exception and inturn has no exception handler. So it passes back to where it came from !
pradeep's Avatar, Join Date: Apr 2005
Team Leader
Well, this is JavaScript not Java, both are very much different!
kush_2207's Avatar, Join Date: Jun 2007
Go4Expert Member
oopss...sorry posted without reading the title anyways thanks for your information.
LMatta's Avatar, Join Date: Jun 2007
Light Poster
Which is the best book for beginners to read Javascript
LMatta's Avatar, Join Date: Jun 2007
Light Poster
This Article is Awesome.... Able to understand it very clearly..
pradeep's Avatar, Join Date: Apr 2005
Team Leader
Well I don't know about any such book, check the resources listed in the Javascript forums here!