JavaScript error messages, error handling and try catch

To avoid errors being presented to the end user:

function doNothing() {return true;}
 window.onerror = doNothing;

But of course, the best way to handle this (after IE 5), is by using try{ } catch { } structures:

<script type=”text/javascript” language=”JavaScript1.5″>
  function myFunc() {
      try {
          // statement(s) that could throw an error if various conditions aren’t right
      }
      catch(e) {
          // statements that handle the exception (error object passed to e variable)
      }
  }
  </script>

Note how the script has to be set as javascript1.5 to avoid old browsers to run into problems with try catch.

The following table indicates what’s available from the “e” error object passed to the catch statement, and what browsers support it:

Property
IE/Windows
Mozilla
Safari
Opera
Description
 
 
 


description
5
n/a
n/a
n/a
Plain-language description of error
 


fileName
n/a
all
n/a
n/a
URI of the file containing the script throwing the error 


lineNumber
n/a
all
n/a
n/a
Source code line number of error
 


message
5.5
all
all
7
Plain-language description of error (ECMA)
 


name
5.5
all
all
7
Error type (ECMA)
 
 
 


number
5
n/a
n/a
n/a
Microsoft proprietary error number
 


stack
n/a
1.0.1
n/a
n/a
Multi-line string of function references leading to error


 From inside a try statement, you can throw errors yourself:

throw err;