JavaScript try/catch: errors or exceptions?

Question

OK. I may be splitting hairs here, but my code isn't consistent and I'd like to make it so. But before I do, I want to make sure I'm going the right way. In practice this doesn't matter, but this has been bothering me for a while so I figured I'd ask my peers...

Every time I use a try... catch statement, in the catch block I always log a message to my internal console. However my log messages are not consistent. They either look like:

catch(err) {
DFTools.console.log("someMethod caught an error: ",err.message);
...

or:

catch(ex) {
DFTools.console.log("someMethod caught an exception: ",ex.message);
...

Obviously the code functions properly either way but it's starting to bother me that I sometimes refer to "errors" and sometimes to "exceptions". Like I said, maybe I'm splitting hairs but which is the proper terminology? "Exception", or "Error"?

Answer 1

What you get in a Catch block is an Exception, so I name it as an exception...

If it is an error - I can handle it in my code & I usually don't expect to see it in the Catch block

HTH.

Answer 2

Exception is something you may expected for example in an attempt to open a file may face a "File not found exception". On the other hand, errors are something you may not see it coming like stack over flow or not enough memory.

An exception is an alternative logical way out off a function that does not produce a logical result. An exception also allows a better explanation of what happen why it exist this way. For File opening, again, a file handle is a logical result and if the file is not exist (one possible exception) or it is a folder not a file (another possible exception).

Answer 3

In JavaScript it is called Error Catching. So I would suggest you use error instead of exception. Leave the choice in the middle by using "e". Like in the examples of Mozilla. Mozilla Core JavaScript 1.5 Reference

Answer 4

This is a bit subjective, but to me an error is when someone or something does something wrong, improper, or invalid. It could be a syntax error, a logical error, a read error, user error, or even a social error. It's an abstract concept.

An exception, on the other hand, is an object that is created and thrown when a certain condition occurs in code. It may or may not correspond to a conceptual error. So to me, the proper nomenclature is "exception".

Answer 5

The ECMAScript specification calls them exceptions. You might want to do likewise.

To make your logging more informative:

catch(ex) {
    DFTools.console.log("someMethod caught an exception of type " 
       + ex.name + ": ", ex.message);

You might also want to bear in mind that exceptions (unfortunately) can be of any type, and so don't necessarily have name and message properties:

catch(ex) {
    if (ex.message && ex.name) {        
        DFTools.console.log("someMethod caught an exception of type " 
           + ex.name + ": ", ex.message);
    } else /* deal with it somehow */

As this is starting to look pretty cumbersome to repeat everywhere, you might want to capture it in a function:

function logExceptions(methodName, action) {

    try {

        action();

    } catch (ex) {
        if (ex.message && ex.name) {        
            DFTools.console.log("someMethod caught an exception of type " 
               + ex.name + ": ", ex.message);
        } else {
            DFTools.console.log("someMethod caught a poorly-typed exception: " + ex);
        }
    }
}

Now you can say:

logExceptions(function() {

    // do some risky stuff...

});