Below is the sample JavaScript logic. I have explained best practices how to use Try, Catch and Throw.
Java Script Error Handling best Practices
<SCRIPT LANGUAGE=”JavaScript” TYPE=”text/javascript”>
function getMonthName (monthNumber) {
// JavaScript arrays begin with 0, not 1, so
// subtract 1.
monthNumber = monthNumber - 1
// Create an array and fill it with 12 values
var months = new Array(“Jan”,”Feb”,”Mar”,”Apr”,”May”,”Jun”,”Jul”,
“Aug”,”Sep”,”Oct”,”Nov”,”Dec”)
// If the monthNumber passed in is somewhere
// between 0 and 11, fine; return the corresponding
// month name.
if (months[monthNumber] != null) {
return months[monthNumber]
}
// Otherwise, an exception occurred, so throw
// an exception.
250 Part IV: Interacting with Users
21_576593 ch14.qxd 10/12/04 10:02 PM Page 250
else {
// This statement throws an error
// directly to the catch block.
throw “InvalidMonthNumber”
}
}
//////////////////////////////////////////////////////
// The try block wraps around the main JavaScript
// processing code. Any JavaScript statement inside
// the try block that generates an exception will
// automatically throw that exception to the
// exception handling code in the catch block.
//////////////////////////////////////////////////////
// The try block
try {
// Call the getMonthName() function with an
// invalid month # (there is no 13th month!)
// and see what happens.
alert(getMonthName(13))
alert(“We never get here if an exception is thrown.”)
}
// The catch block
catch (error) {
alert(“An “ + error + “ exception was encountered. Please contact the
program vendor.”)
// In a real-life situation, you might want
// to include error-handling code here that
// examines the exception and gives users specific
// information (or even tries to fix the problem,
// if possible.)
}
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