How can I allow the '-' sign on an empty input with ng2-currency-mask in Angular?

Below is an explanation of the current limitation and some alternatives you might consider:

Limitation in ng2-currency-mask

The ng2-currency-mask library is designed so that the negative sign (‑) is only allowed when there’s at least one digit present. In other words, the library’s input formatting logic prevents you from starting with a "-" on an empty field. There isn’t a built‐in configuration option to change this behavior.

Possible Workarounds

1. Customizing the Directive or Source Code:
   You mentioned trying a custom directive (e.g., on keydown) to allow "-" when the field is empty. Unfortunately, the underlying mask implementation seems to veto that input. One option is to fork or patch the library's source to modify how it processes the negative sign. This approach would require a deep dive into the library’s formatter logic.

2. Using Alternative Libraries:
   If forking the library isn’t desirable, consider using a different library or approach. Some alternatives include:

   • ngx-currency: This library intentionally offers currency formatting for Angular and might provide the flexibility you need (including support for leading '-' in an empty field).
   • Custom Input with Angular Pipes: Instead of relying on a third‑party mask, you might implement a custom input component that uses Angular’s reactive forms together with the built‑in currency pipe (or a third‑party pipe) to format numbers. This gives you total control over the input behavior.

Summary

Currently, with ng2‑currency‑mask, there is no out‑of‑the‑box way to allow entering "-" on an empty text field. For your requirements, the recommended alternatives are either to modify the library (which can be quite involved) or to switch to a different library like ngx‑currency that might better accommodate the behavior you want.

Feel free to ask for further details on either customizing the input or using one of the alternative libraries!