getify/gist:297845

## gistfile1.htm
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Custom Error Objects in JavaScript</title>
</head>
<body>

<h1>Custom Error Objects in JavaScript</h1>

<form>
<textarea id="thelog" name="thelog" cols="50" rows="15"></textarea>
</form>


<script>
// howto: subclass/extend built-in Error object, courtesy @jdalton

var MyError = (function() {
	function F(){}
	function CustomError() {
		var _this = (this===window) ? new F() : this, // correct if not called with "new"
			tmp = Error.prototype.constructor.apply(_this,arguments)
		;
		for (var i in tmp) {
			if (tmp.hasOwnProperty(i)) _this[i] = tmp[i];
		}
		return _this;
	}
	function SubClass(){}
	SubClass.prototype = Error.prototype;
	F.prototype = CustomError.prototype = new SubClass();
	CustomError.prototype.constructor = CustomError;

	// add a custom method
	CustomError.prototype.CustomField1 = function(custom_1){
		if (custom_1 != null) this.custom_1 = custom_1;
		return this.custom_1;
	}

	return CustomError;
})();

var MoreMyError = (function() {
	function F(){}
	function CustomError() {
		var _this = (this===window) ? new F() : this, // correct if not called with "new"
			tmp = MyError.prototype.constructor.apply(_this,arguments)
		;
		for (var i in tmp) {
			if (tmp.hasOwnProperty(i)) _this[i] = tmp[i];
		}
		return _this;
	}
	function SubClass(){}
	SubClass.prototype = MyError.prototype;
	F.prototype = CustomError.prototype = new SubClass();
	CustomError.prototype.constructor = CustomError;

	// override inherited custom method
	CustomError.prototype.CustomField1 = function(custom_1){
		if (custom_1 != null) this.custom_1 = custom_1;
		return this.custom_1.toUpperCase();
	}

	// add another custom method
	CustomError.prototype.CustomField2 = function(custom_2){
		if (custom_2 != null) this.custom_2 = custom_2;
		return this.custom_2;
	}

	return CustomError;
})();

function logit(msg) {
	document.getElementById("thelog").value += msg + "\n";
}


var err = Error("{native Error}");	// or better, new Error(...)
logit("[err]message:"+err.message);
logit("[err]instanceof Error:"+(err instanceof Error));
logit("");


var err2 = MyError("{custom MyError}");	// or better, new MyError(...)
err2.CustomField1("custom1");
logit("[err2]message:"+err2.message);
logit("[err2]custom_field_1:"+err2.CustomField1());
logit("[err2]instanceof Error:"+(err2 instanceof Error));
logit("[err2]instanceof MyError:"+(err2 instanceof MyError));
logit("");


var err3 = MoreMyError("{custom MoreMyError}");	// or better, new MoreMyError(...)
err3.CustomField1("custom1");
err3.CustomField2("custom2");
logit("[err3]message:"+err3.message);
logit("[err3]custom_field_1:"+err3.CustomField1());
logit("[err3]custom_field_2:"+err3.CustomField2());
logit("[err3]instanceof Error:"+(err3 instanceof Error));
logit("[err3]instanceof MyError:"+(err3 instanceof MyError));
logit("[err3]instanceof MoreMyError:"+(err3 instanceof MoreMyError));

</script>

</body>
</html>
	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<title>Custom Error Objects in JavaScript</title>
	</head>
	<body>

	<h1>Custom Error Objects in JavaScript</h1>

	<form>
	<textarea id="thelog" name="thelog" cols="50" rows="15"></textarea>
	</form>


	<script>
	// howto: subclass/extend built-in Error object, courtesy @jdalton

	var MyError = (function() {
	function F(){}
	function CustomError() {
	var _this = (this===window) ? new F() : this, // correct if not called with "new"
	tmp = Error.prototype.constructor.apply(_this,arguments)
	;
	for (var i in tmp) {
	if (tmp.hasOwnProperty(i)) _this[i] = tmp[i];
	}
	return _this;
	}
	function SubClass(){}
	SubClass.prototype = Error.prototype;
	F.prototype = CustomError.prototype = new SubClass();
	CustomError.prototype.constructor = CustomError;

	// add a custom method
	CustomError.prototype.CustomField1 = function(custom_1){
	if (custom_1 != null) this.custom_1 = custom_1;
	return this.custom_1;
	}

	return CustomError;
	})();

	var MoreMyError = (function() {
	function F(){}
	function CustomError() {
	var _this = (this===window) ? new F() : this, // correct if not called with "new"
	tmp = MyError.prototype.constructor.apply(_this,arguments)
	;
	for (var i in tmp) {
	if (tmp.hasOwnProperty(i)) _this[i] = tmp[i];
	}
	return _this;
	}
	function SubClass(){}
	SubClass.prototype = MyError.prototype;
	F.prototype = CustomError.prototype = new SubClass();
	CustomError.prototype.constructor = CustomError;

	// override inherited custom method
	CustomError.prototype.CustomField1 = function(custom_1){
	if (custom_1 != null) this.custom_1 = custom_1;
	return this.custom_1.toUpperCase();
	}

	// add another custom method
	CustomError.prototype.CustomField2 = function(custom_2){
	if (custom_2 != null) this.custom_2 = custom_2;
	return this.custom_2;
	}

	return CustomError;
	})();

	function logit(msg) {
	document.getElementById("thelog").value += msg + "\n";
	}


	var err = Error("{native Error}"); // or better, new Error(...)
	logit("[err]message:"+err.message);
	logit("[err]instanceof Error:"+(err instanceof Error));
	logit("");


	var err2 = MyError("{custom MyError}"); // or better, new MyError(...)
	err2.CustomField1("custom1");
	logit("[err2]message:"+err2.message);
	logit("[err2]custom_field_1:"+err2.CustomField1());
	logit("[err2]instanceof Error:"+(err2 instanceof Error));
	logit("[err2]instanceof MyError:"+(err2 instanceof MyError));
	logit("");


	var err3 = MoreMyError("{custom MoreMyError}"); // or better, new MoreMyError(...)
	err3.CustomField1("custom1");
	err3.CustomField2("custom2");
	logit("[err3]message:"+err3.message);
	logit("[err3]custom_field_1:"+err3.CustomField1());
	logit("[err3]custom_field_2:"+err3.CustomField2());
	logit("[err3]instanceof Error:"+(err3 instanceof Error));
	logit("[err3]instanceof MyError:"+(err3 instanceof MyError));
	logit("[err3]instanceof MoreMyError:"+(err3 instanceof MoreMyError));

	</script>

	</body>
	</html>