I just want to add to what others have already stated:

To make sure that the custom error class shows up properly in the stack trace, you need to set the custom error class's prototype's name property to the custom error class's name property. This is what I mean:

CustomError.prototype = Error.prototype;
CustomError.prototype.name = 'CustomError';

So the full example would be:

    var CustomError = function(message) {
        var err = new Error(message);
        err.name = 'CustomError';
        this.name = err.name;
        this.message = err.message;
        //check if there is a stack property supported in browser
        if (err.stack) {
            this.stack = err.stack;
        }
        //we should define how our toString function works as this will be used internally
        //by the browser's stack trace generation function
        this.toString = function() {
           return this.name + ': ' + this.message;
        };
    };
    CustomError.prototype = Error.prototype;
    CustomError.prototype.name = 'CustomError';

When all is said and done, you throw your new exception and it looks like this (I lazily tried this in the chrome dev tools):

CustomError: Stuff Happened. GASP!
    at Error.CustomError (<anonymous>:3:19)
    at <anonymous>:2:7
    at Object.InjectedScript._evaluateOn (<anonymous>:603:39)
    at Object.InjectedScript._evaluateAndWrap (<anonymous>:562:52)
    at Object.InjectedScript.evaluate (<anonymous>:481:21)

I just want to add to what others have already stated:

To make sure that the custom error class shows up properly in the stack trace, you need to set the custom error class's prototype's name property to the custom error class's name property. This is what I mean:

CustomError.prototype = Error.prototype;
CustomError.prototype.name = 'CustomError';

So the full example would be:

    var CustomError = function(message) {
        var err = new Error(message);
        err.name = 'CustomError';
        this.name = err.name;
        this.message = err.message;
        //check if there is a stack property supported in browser
        if (err.stack) {
            this.stack = err.stack;
        }
        //we should define how our toString function works as this will be used internally
        //by the browser's stack trace generation function
        this.toString = function() {
           return this.name + ': ' + this.message;
        };
    };
    CustomError.prototype = new Error();
    CustomError.prototype.name = 'CustomError';

When all is said and done, you throw your new exception and it looks like this (I lazily tried this in the chrome dev tools):

CustomError: Stuff Happened. GASP!
    at Error.CustomError (<anonymous>:3:19)
    at <anonymous>:2:7
    at Object.InjectedScript._evaluateOn (<anonymous>:603:39)
    at Object.InjectedScript._evaluateAndWrap (<anonymous>:562:52)
    at Object.InjectedScript.evaluate (<anonymous>:481:21)