Throwing custom exceptions in Javascript. Which style to use?

Question

Douglas Crockford recommends doing something like this:

throw {     name: "System Error",     message: "Something horrible happened." }; 

But you could also do something like this:

function IllegalArgumentException(message) {     this.message = message; }  throw new IllegalArgumentException("Argument cannot be less than zero"); 

and then do:

try {     //some code that generates exceptions } catch(e) {         if(e instanceof IllegalArgumentException) {         //handle this     } else if(e instanceof SomeOtherTypeOfException) {         //handle this     } } 

I guess you could include a type property in Crockford's implementation and then examine that instead of doing an instanceof. Is there any advantage from doing one versus the other?

Answer 1

Please note that meanwhile most of the JavaScripts environments provide the Error object as basis for exceptions. It already allows you to define a message, but also provides a useful stack property to track down the context of the exception. You can create your own exception type by using prototypical inheritance. There are already several stackoverflow discussions (for example: here), how to do this properly. However, I had to dig a little bit until I found the correct and modern approach. Please be aware that the approach that is suggested in the Mozilla documentation (see above) is not liked by the stackoverflow community. After a lot of reading I came out with that approach for inherit from Error.prototype:

function IllegalArgumentException(sMessage) {     this.name = "IllegalArgumentException";     this.message = sMessage;     this.stack = (new Error()).stack; } IllegalArgumentException.prototype = Object.create(Error.prototype); IllegalArgumentException.prototype.constructor = IllegalArgumentException;