Getting the stack trace of an error

Hi dln385,

I have no answer for your question but what your code reveals is very educative: the throw statement always triggers the toString() method of the throwed object. I never realized that.

// Throwing obj causes obj.toString() invokation
//--------------------------------------
var obj = {
    toString: function(){ alert("Hello guys!"); }
    };
try{ throw obj; } // => Hello guys!
catch(_){}

Another fact I noticed is that throwing anything binds the caught reference to anything, whatever it refers to:

// What you throw is what you catch!
//--------------------------------------
var anything = {}; // works with literals too, e.g. "foobar", or even 5!
try{ throw anything; }
catch(e){ alert( e===anything ); }  // true!

For these reasons the actual Error(...) constructor—which basically behaves as a simple {message, name, etc.} object factory—doesn't seem essential to the try/throw/catch trio. Therefore, as long as you need to handle custom exceptions, you could as well entirely bypass the native Error object:

// No need to use native Error class
//--------------------------------------
function MyException(msg,s)
{
    this.message = msg || '';
    this.name = s || 'Error';
    this.stack = null;
};
MyException.prototype.toString = function()
{
    // Hook $.stack *on first invokation*
    // ---
    this.stack || (this.stack = $.stack.
                replace(/[\r\n]toString\(\)[\r\n]$/,'').
                split(/[\r\n]/)
                );
    // Make toString() ECMA-262 compliant
    // ---
    return this.name + ': ' + this.message;
};
// =================
// Example code
// =================
function inner()
{
    throw new MyException("Something's gone wrong!");
}
function outer()
{
    inner();
}
function main()
{
    try{ outer(); }
    catch(e)
        {
        alert( e );        // => Error: Something's gone wrong!
        alert( e.stack );  // => [myScript.jsx],main(),outer(),inner()
        }
}
main();

Now, your original question still remains, about built-in Error types (Error, EvalError, RangeError, ReferenceError, SyntaxError, TypeError, URIError). The fact is that ExtendScript does not invoke Error.prototype.toString() when a "native error" occurs. The opposite would be somewhat embarrassing!

// Pure errors (not explicitly thrown) do not involve toString
//--------------------------------------
// Disclaimer: overriding Error.prototype
// is not recommended at all!
Error.prototype.toString = function(){ alert( "Hello guys!" ); };
// Let's cause a RangeError...
try {
    new Array(-1); // silent!
    }
catch(e)
    {
    alert( e.name ); // => RangeError
    }
// By contrast:
try {
    throw new Error("My error"); // => Hello guys!
    }
catch(e)
    {
    alert( e.name ); // => Error
    }

Hope that may help a bit.

@+

Marc

hei!

In extendscript there are some problems when extending some objects. Not sure it Error is one of them, but your problem sure looks like that.

Here is a great source of info:

http://forums.adobe.com/message/4133138#4133138