LWC Global Uncaught Promise Error Handler

Question

I am trying to implement a global uncaught promise error handler for a lightning web component. The goal is to reduce the catch(error) statements for promises:

getDocumentTypes() {
    getDocumentTypes({ load: this.load })
    .then(result => {      
        LightningUtil.processMessagesAndErrors2(this, result);   
        if(result.IsOK) {
            this.documentTypes = result.Payload;  
        }
    })
    .catch(error => {
        LightningUtil.logError(this, error);
    });
}

I tried to implement an unhandledrejection event listener in an LWC:

constructor() {
    super();        
    window.addEventListener('unhandledrejection', this.myFunction);
}

But the following error occurs in the console: Uncaught (in promise) Error: Lightning Web Security: Cannot add 'unhandledrejection' event listener to Window object.

Is this a limitation of the LWC SecureWindow and is there any other way to implement a global uncaught promise error handler?

Answer 1

If you were allowed to catch any error, you might be able to catch another component's uncaught exceptions. This is a LWS (Lightning Web Security) enhancement.

In the LWS distortion viewer, it says:

The unhandledrejection event is sent to the global scope of a script when a JavaScript Promise that has no rejection handler is rejected; typically, this is the window, but may also be a Worker.

This is useful for debugging and for providing fallback error handling for unexpected situations.

The event object associated with the unhandledrejection event exposes a property called reason, which can contain sensitive information.

Distorted Behavior

Currently, Lightning Web Security doesn't support setting the onunhandledrejection event handler or adding a unhandledrejection event listener; attempting to do so throws an exception.

Interestingly, this is only a problem with LWS, as the Locker API Viewer says:

Window vs SecureWindow Compatibility

onunhandledrejection

Prototype: Window

Supported

Version 46

In other words, SecureWindow does actually support this. It is likely that LWS may end up supporting this mechanism in the long term, but I can't find any documentation that backs this up.

You should be able to, however, set a boundary component that can handle all errors. This is the errorCallback part of the LWC lifecycle. This function receives a JavaScript error object, and a stack trace as a string. You can wrap your components with a border component to handle errors in a generic manner.