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JavaScript Tutorial

  1. JavaScript Browser Objects Part 2
  2. JavaScript Frame object
  3. JavaScript Form Object
  4. JavaScript FileUpload Object
  5. JavaScript Event Object Properties and Methods
  6. JavaScript Event Object
  7. JavaScript Elements and Embed Objects
  8. JavaScript Applet Objects
  9. JavaScript Browser Objects
  10. JavaScript Object Oriented Features
  11. JavaScript Window Object Open Method Part 2
  12. JavaScript Window Object Open Method
  13. JavaScript Window Object Timeout Methods
  14. JavaScript Location Object
  15. JavaScript Location Object Properties
  16. JavaScript History Object Properties and Methods
  17. JavaScript Document Object Methods Part II
  18. JavaScript Document Object Methods Part I
  19. JavaScript Document Object Properties
  20. JavaScript Document Object
  21. JavaScript Windows Object Properties Part II
  22. JavaScript Windows Object Properties Part I
  23. JavaScript DOM Window Object
  24. Working with JavaScript DOM Objects
  25. JavaScript Array Object Methods – Part II
  26. JavaScript Array Object
  27. JavaScript Array Object Methods – Part I
  28. JavaScript Boolean Object
  29. JavaScript OnError Event
  30. JavaScript Exception Handling – Part II
  31. JavaScript Exception Handling – Part I
  32. JavaScript Event Handler
  33. JavaScript Events Handling
  34. JavaScript Array Operations
  35. JavaScript Two Dimensional Arrays
  36. Passing values to JavaScript Function
  37. JavaScript Functions
  38. JavaScript Arrays
  39. JavaScript Iterative Structures - Part II
  40. JavaScript Iterative Structures - Part I
  41. JavaScript Math Object
  42. JavaScript Date Object
  43. JavaScript String Object
  44. JavaScript Objects
  45. JavaScript Confirm Box
  46. JavaScript Alert Box
  47. JavaScript Conditional Statements Part 2
  48. JavaScript Conditional Statements Part 1
  49. How to use JavaScript in HTML page
  50. JavaScript Variables
  51. JavaScript Features
  52. JavaScript Introduction

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Home arrow Technical Training arrow JavaScript Tutorial

JavaScript Exception Handling – Part II

Author : Exforsys Inc.     Published on: 2nd Aug 2007

JavaScript Exception Handling – Part II

In this JavaScript tutorial, you will learn about exception handling viz. try…catch..finally statement and nested try…catch statements along with syntax and examples.

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try…catch..finally Statement:

JavaScript has a finally statement that can be used as an optional construct along with try..catch statements. The finally construct placed in a try…catch construct is an optional statement. When the finally statement is placed in a try…catch construct, it always runs following the try…catch structure.

The general syntax of a try…catch..finally statement is as follows:


try
{
…………      
//Block of code which is to be tested for errors
…………
}
catch(err)
{
…………
…………     
//Block of code which is to be executed if an error occurs
}
finally
{
…………
…………    
//This is optional and runs after try and catch structure has run.
}

 

for example:

 


<html>
   <
head>
      <
script type="text/javascript">
        try
        {
           document.write(junkVariable)
        }

        catch(err)
        {
           document.write(err.message + "<br/>")
        }
        finally
        {
           document.write("Finally Block entered: Welcome")
        }

      </
script>
   <
/head>

   <
body>
   </
body>
</
html>

The output of the above program is

‘junkVariable’ is undefined
Finally Block entered: Welcome

In the above program, after the try block is executed, the catch block throws the error. The finally statement is then executed last, displaying the second message “Finally Block entered: Welcome”

Additional usage information about try…catch..finally and throw statements:

Nested try…catch Statements:

It is also possible to have nested try..catch statements or one try..catch statement placed inside another.

for example:


try{
      .........           
//Block of code
      .........           
//Block of code
      try
      {
         .........        
//Block of code
         .........        
//Block of code
      }
      catch(Err)
      {
         ........         
//Block of code
         ........         
//Block of code
      }
      ........           
 //Block of code
      ........           
 //Block of code
}
catch(err1)
{
     ........           
    //Block of code
     ........             
//Block of code
}

finally

{

     ........                //Block of code
     ........             
//Block of code
}

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* It is also possible to catch the error placed in the inner try..catch statement, then use that error in the outer catch statement of the nested try..catch statement using the throw statement of JavaScript.

* Using the throw statement, it is possible for the programmer to throw errors at any point.



 
This tutorial is part of a JavaScript Tutorial tutorial series. Read it from the beginning and learn yourself.

JavaScript Tutorial

  1. JavaScript Browser Objects Part 2
  2. JavaScript Frame object
  3. JavaScript Form Object
  4. JavaScript FileUpload Object
  5. JavaScript Event Object Properties and Methods
  6. JavaScript Event Object
  7. JavaScript Elements and Embed Objects
  8. JavaScript Applet Objects
  9. JavaScript Browser Objects
  10. JavaScript Object Oriented Features
  11. JavaScript Window Object Open Method Part 2
  12. JavaScript Window Object Open Method
  13. JavaScript Window Object Timeout Methods
  14. JavaScript Location Object
  15. JavaScript Location Object Properties
  16. JavaScript History Object Properties and Methods
  17. JavaScript Document Object Methods Part II
  18. JavaScript Document Object Methods Part I
  19. JavaScript Document Object Properties
  20. JavaScript Document Object
  21. JavaScript Windows Object Properties Part II
  22. JavaScript Windows Object Properties Part I
  23. JavaScript DOM Window Object
  24. Working with JavaScript DOM Objects
  25. JavaScript Array Object Methods – Part II
  26. JavaScript Array Object
  27. JavaScript Array Object Methods – Part I
  28. JavaScript Boolean Object
  29. JavaScript OnError Event
  30. JavaScript Exception Handling – Part II
  31. JavaScript Exception Handling – Part I
  32. JavaScript Event Handler
  33. JavaScript Events Handling
  34. JavaScript Array Operations
  35. JavaScript Two Dimensional Arrays
  36. Passing values to JavaScript Function
  37. JavaScript Functions
  38. JavaScript Arrays
  39. JavaScript Iterative Structures - Part II
  40. JavaScript Iterative Structures - Part I
  41. JavaScript Math Object
  42. JavaScript Date Object
  43. JavaScript String Object
  44. JavaScript Objects
  45. JavaScript Confirm Box
  46. JavaScript Alert Box
  47. JavaScript Conditional Statements Part 2
  48. JavaScript Conditional Statements Part 1
  49. How to use JavaScript in HTML page
  50. JavaScript Variables
  51. JavaScript Features
  52. JavaScript Introduction
 

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