There is no way to property deal with exceptions in CoreViewer

[depth42]

I am using the CoreViewer.loadDocument API for loading documents and I use the addListener API to get notified when loading has finished. When because of any reason Vivliostyle is throwing an exception during pagination, there is no way for me to detect this, as Vivliostyle simply catches and logs the exception but the listener is not notified.

[MurakamiShinyu]

Vivliostyle Viewer can display error messages. The relevant code is found in:

vivliostyle.js/packages/viewer/src/viewmodels/viewer.ts

Lines 119 to 121 in 8667886

	this.coreViewer.addListener("error", (payload) => {
	logger.error(payload.content);
	});

vivliostyle.js/packages/viewer/src/logging/logger.ts

Line 75 in 8667886

error(content: unknown): void {

vivliostyle.js/packages/viewer/src/viewmodels/message-dialog.ts

Line 41 in 8667886

getDisplayMessage(errorInfo: ErrorInfo): string {

You may write similar code in your program that uses the CoreViewer. e.g.,

  coreViewer.addListener("error", (payload) => {
    alert(payload.content.error);
  });

[depth42]

Thank you. Is it guaranteed, that Vivliostyle stops pagination with the first error that occurs? Or can there be more than one error?

[MurakamiShinyu]

There can be more than one error. However, "error" indicates something unexpected, e.g., "TypeError: Cannot read properties of undefined" is caused by program bugs and after such an exception occurs, normal processing is not expected to continue.

On the other hand, "warn" (you can use .addListener("warn", …)) indicates something wrong such as invalid or unsupported syntax in style sheets, and processing can continue.

[MurakamiShinyu]

Thanks to this issue, I realized that the error handling in vivliostyle, especially on vivliostyle-print, needs to be improved, so I made the following pull requests:

• feat: Add errorCallback config option to VivliostylePrint/printHTML() #1287
• Add errorCallback to demo vivliostyle-print#10