Avoiding an empty catch clause

问题

I have a function which checks to see if the user has made any changes, and if so, warns them of this fact. When they choose to discard their changes, I have another function which a) restores the state to pre-edit, and b) updates a global object which holds info about the current edit (including whether one exists).

What I don't want to happen is that some error is thrown on trying to remove the edit box elements, and as a result the system doesn't update the global object flag or show the hidden pre-edit elements. If this happens, the program may think an edit is still going on when it isn't, leaving the user trapped in a "Discard changes?" cycle. For this reason, I catch any errors thrown in the destroy phase, and then show the hidden elements and update the global, like this:

function cancelEdit() {

    try {
        // destroy editing boxes
        // [code goes here]
    } catch(e) {
    } finally {
        // restore hidden elements
        // [code goes here]

        // update global edit cache object
        // [code goes here]

        // rethrow the error for analysis server-side
        if(window.onerror) window.onerror();
    }

}

Having an empty catch block like above seems like a code smell to me, but I don't think this way is necessarily better. (But maybe it is.)

function cancelEdit() {

    try {
        // destroy editing boxes
        // [code goes here]
    } catch(e) {
        cancelEditInternal();
        // rethrow the error for analysis server-side
        throw e;
    }

    cancelEditInternal();

}

function cancelEditInternal() {

    // restore hidden elements
    // [code goes here]

    // update global edit cache object
    // [code goes here]

}

Am I missing something? Is there a pattern that I'm neglecting... or is this just a consequence of the fact that I'm using try/catch/finally where it isn't usually used?

回答1:

You can use a finally block:

function cancelEdit() {
    try {
        // destroy editing boxes
        // [code goes here]
    } finally {
        cancelEditInternal();
    }

}

The finally block will be executed whether or not the body of the try throws an error. (If you keep the catch clause, the finally block will still execute.)

回答2:

If you don't want the catch block, then don't use it:

try {
    // destroy editing boxes
    // [code goes here]
} finally {
    // restore hidden elements
    // [code goes here]

    // update global edit cache object
    // [code goes here]

    // rethrow the error for analysis server-side
    if(window.onerror) window.onerror();
}

As you can see in the specification, a try statement consist of try followed by either catch or finally or both.

来源：https://stackoverflow.com/questions/26537048/avoiding-an-empty-catch-clause

标签

javascript

try-catch-finally