Web Page Error Handling Comparison

Michael D. Edwards
Software Design Engineer
Microsoft Corporation

March 11, 1999

The following table compares the error-handling techniques discussed in "Handling and Avoiding Web Page Errors Part 2: Run-time Errors".

Error Handling Technique	Cross-Browser	Can Resume Execution	Errors Handled	Can Pass Error to other Handler	Can Define Custom Errors
window.onerror	Navigator 3.x, 4.x, 5 Internet Explorer 4.x, 5	no, further execution is aborted until next user action or handled event	handles all run-time script errors not already handled via other techniques	from custom handler to default handler via DHTML event bubbling	DHTML event model is not customizable
ECMAScript 2.0   JavaScript 1.4   JScript 5.0	Navigator 51 Internet Explorer 5	execution resumes in catch block and then optional finally block	handles run-time script errors only within try blocks	try...catch blocks can be nested, use throw to pass up the chain2	throw argument can be any user-defined string, number or object variable
VBScript	Internet Explorer 3.x, 4.x, 53	execution resumes on line following line that caused error (user must check for error with if statement)	enabled by On Error Resume Next, active for all remaining statements in procedure or <SCRIPT> block, or until On Error Goto 0	user controls whether to invoke error handler where errors occur, or at higher level (in the caller)	Err.Raise initializes Err object properties to user-defined values

¹JavaScript 1.4 lacks support for handling run-time errors from the script engine

²window.onerror handler is invoked if throw from highest-order try...catch block

³VBScript is not supported on the Mac OS