Proper way to subclass Error
Jeff Watkins
like to be able to capture uncaught exceptions and display the correct
stack trace. However, for my custom exceptions, the stack trace is
showing the point at which I create the prototype Error rather than
the instance.
1 coherent.defineError= function( errorName )
2 {
3 constructor= function( message )
4 {
5 this.message= message;
6 }
7
8 constructor.prototype= new Error;
9 constructor.prototype.constructor= constructor;
10 constructor.prototype.name= errorName;
11 return constructor;
12 }
13
14 var InvalidArgumentError=
coherent.defineError( "InvalidArgumentError" );
When I create a new InvalidArgumentError instance, the stack indicates
that the error was created on line 8 rather than where ever it was in
the actual code.
What's the proper way to do this?
--
Jeff Watkins
http://metrocat.org
Computers, they're just a fad.
Ash Berlin
There's 2 ways of doing this:
constructor= function( message ) {
this.stack = (new Error).stack
}
Or if you dont mind it not being portable with other JS implementations
constructor.prototype = Error.__proto__
I *think* something like that should work.
Ash
Ash Berlin
On Jan 3, 2008, at 6:27 PM, Jeff Watkins wrote:
> Unfortunately, the first way leads to the stack listing the
> constructor as the place where the error was thrown. And the second
> way just simply didn't seem to work – the custom error didn't seem
> to work correctly.
>
> It's not the end of the world, because I really need these tests to
> run in the browser and the stack doesn't work there unless you're
> running FF.
>
> On 3 Jan, 2008, at 4:26 AM, Ash Berlin wrote:
>
>> There's 2 ways of doing this:
>>
>> constructor= function( message ) {
>> this.stack = (new Error).stack
>> }
>>
>> Or if you dont mind it not being portable with other JS
>> implementations
>>
>> constructor.prototype = Error.__proto__
>>
>> I *think* something like that should work.
Okay then...
metis:~ ash$ cat test.js
var coherent = {};
coherent.defineError = function(errorName)
{
constructor = function() {
stack = (new Error).stack.split("\n").slice(1);
[undef, undef, this.fileName, this.lineNumber] =
/^(.*?)@(.*?):(.*?)$/.exec( stack[1] );
this.stack = stack.join("\n");
};
constructor.prototype = {
__proto__: Error.prototype,
name: errorName,
};
return constructor;
}
var InvalidArgumentError =
coherent.defineError( "InvalidArgumentError" );
var err = (new InvalidArgumentError('abc'));
var err2 = new Error("an error");
print(err.lineNumber);
print(err2.lineNumber);
metis:~ ash$ ./code/js/mozilla/dist/bin/js -f test.js
20
21
That might do what you want....