> For the complete documentation index, see [llms.txt](https://strctr.gitbook.io/programming/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://strctr.gitbook.io/programming/01-languages/javascript/01-language/e-controls/e2-exception-handling/03-conditional-catch-clauses.md).

# 03 Conditional Catch

Sometimes you may need to have one or more conditional catch clauses to handle specific exceptions:

```javascript
try {
  myroutine(); // may throw three types of exceptions
} catch (e) {
  if (e instanceof TypeError) {
    // statements to handle TypeError exceptions
  } else if (e instanceof RangeError) {
    // statements to handle RangeError exceptions
  } else if (e instanceof EvalError) {
    // statements to handle EvalError exceptions
  } else {
    // statements to handle any unspecified exceptions
    logMyErrors(e); // pass exception object to error handler
  }
}
```

## Guard for exceptions

JavaScript catch doesn't support any mechanism to filter errors. This limitation isn't too hard to get around: we can write a function `guard()`:

```javascript
function guard(e, predicate) {
  if (!predicate(e)) throw e;
}
```

And then use it to e.g. only filter "not found" errors when downloading an image:

```javascript
try {
    await downloadImage(url);
} catch (e) {
    guard(e, e => e.code == 404);
    handle404(...);
}
```