Error calling method on NPObject

I’ve had a bit of a problem with a Java Applet running in Safari on Windows. I have JavaScript code which attempts to invoke public methods in the Applet, but whenever I try to call these I get the error “Error calling method on NPObject”.

I’ve read a fair amount of BS “causes” (from things like “it’s a hidden DIV” to “Upgrade your JRE”), none of which proved to the the problem.

The real problem?

Safari doesn’t care if the applet is loaded before trying to invoke the methods.

Under Chrome, Opera, Firefox and even my much hated Internet Explorer, if you try to invoke a method on an applet which hasn’t loaded yet, the JavaScript runtime waits for the applet to complete, and then resumes. Safari does not.

So now, as part of the applet tag’s parameters, I have to include a method name which the applet must invoke in JavaScript, thereby guaranteeing that the applet is loaded and running.

Now I have the problem that apparently Safari is trying to execute JavaScript methods as URLs, thus causing a “Malformed URL” error.


After a bit of experimenting, it seems Safari does not like trying to pass and return non-String values. So, instead of using LiveConnect’s “call” method, you have to use “eval”, and don’t expect to be able to pass object around.

2 thoughts on “Error calling method on NPObject”

Leave a Reply

Your email address will not be published. Required fields are marked *