## setErrorHandler · function

Sets a custom error handler function for errors that occur asynchronously
within reactive scopes (e.g., during updates triggered by proxy changes in
`derive` or | A render functions).

The default handler logs the error to `console.error` and adds a simple
'Error' message div to the DOM at the location where the error occurred (if possible).

Your handler can provide custom logging, UI feedback, or suppress the default
error message.

**Signature:** `(handler?: (error: Error) => boolean) => void`

**Parameters:**

- `handler?: (error: Error) => boolean | undefined` - - A function that accepts the `Error` object.
- Return `false` to prevent adding an error message to the DOM.
- Return `true` or `undefined` (or throw) to allow the error messages to be added to the DOM.

**Examples:**

Custom Logging and Suppressing Default Message
```typescript
A.setErrorHandler(error => {
console.warn('Aberdeen render error:', error.message);
// Log to error reporting service
// myErrorReporter.log(error);

try {
// Attempt to show a custom message in the UI
A('div#Oops, something went wrong!', errorClass);
} catch (e) {
// Ignore errors during error handling itself
}

return false; // Suppress default console log and DOM error message
});

// Styling for our custom error message
const errorClass = A.insertCss('background-color:#e31f00 display:inline-block color:white r:3px padding: 2px 4px;');

// Cause an error within a render scope.
A('div.box', () => {
// Will cause our error handler to insert an error message within the box
noSuchFunction();
})
```