"window.onerror"
The window.onerror javascript handler is typically set by most novice programmers to be: window.onerror=null; however, we can use the variables for the error message, the URL, and the line which was the cause of the error to log this information for use in trouble-shooting. We are able to pass that information to a custom function we have created called: MyError().

"function MyError()"
The MyError function will accept the three variables from the error handler and pass them on to do anything we want with them. What we find it best to do is use the MESSAGE and LINE of the error generated and URL encode the page with a CGI variable. If you don't care for Netscape 4.7x users, this is best set with document.location as a javascript variable. With this info we formulate the Str variable which will be set as the URL to go to in the window.open routine.

function MyError(message,url,line){//Uses ColdFusion
	var Str="/JSErrorSave.cfm?Message="+message+"&myURL=#URLENCODEDFORMAT(CGI.PATH_INFO)#&Line="+line;
	var NewError=window.open(Str,"Error","left=0,top=0,width=1,height=1,status=0,location=0")
}

function MyError(message,url,line){//Uses only javascript
	var Str="/JSErrorSave.cfm?Message="+message+"&myURL="+document.location+"&Line="+line;
	var NewError=window.open(Str,"Error","left=0,top=0,width=1,height=1,status=0,location=0")
}

"window.open()"
The window.open() function is a native function in javascript which allows you to open a new window and size it with specific parameters. In this instance, we are creating a variable called NewError, which is going to be assigned a value if the function is run. We pass the Str value for the URL to go to and create a window called Error. The additional parameters size the window as small as we can so we run a file called JSErrorSave.cfm.

var NewError=window.open(Str,"Error","left=0,top=0,width=1,height=1,status=0,location=0")

"error log routine"
This part is the section which you can use your own creative freedom in saving the error. We do have custom scripts which can be set up to save the information to a database or file in ASP, Perl, or ColdFusion. If you do not have the capacity to create a CGI script to save the Message, URL, and Line to a file or database, you can contract with us to create this custom routine on your server. We do also recommend saving the date & time combination as well as the Unique ID and/or Remote Host IP Address if you create your own script. In our shopping cart, we use this information to track this back to the user's statistics to see if additional problems occurred for that user.

"window.close()"
The last line of the routine for the JSErrorSave.cfm script will be to run a native javascript function called window.close(). At this point, the small window does not need to hang around any longer. Since our site created the new window, we also have the scripting power to close it. This routine makes the user almost unaware that a minor javascript error has occurred. You can create other custom functions to run alerts or redirect the parent page to another location using window.opener.location='someOtherPage.cfm' if you detect certain types of errors occurring.