Primary eng (and PM) emails
The Window.showModalDialog API has been deprecated since M35 (and disabled by default since M37). We committed to keeping the implementation until end of April 2015. By that time, M42 will be the current stable channel, so we should follow through with our plan and remove it from M43.
As detailed in the blog posts above, keeping this API would expose our users to a considerable security risk. Furthermore, the implementation results in a lot of code complexity, so just keeping it behind a flag is not a long term solution either.
We decided to support the API behind a flag for an extended deprecation period to allow for updating affected web apps. Now that this period is over, we should follow through and remove the API.
The compatibility risk of this change is considerable as it is difficult to polyfill showModalDialog due to the modal nature, and will require in many cases considerable effort to redesign web sites around asynchronous alternatives.
Alternative implementation suggestion for web developers
It won't be possible to polyfill this API 100%. Web developers will have to rewrite their applications to not depend on the blocking nature of this API. Using the <dialog> element, and ES6 generator functions it is possible to get somewhat similar behavior, see e.g. https://github.com/niutech/showModalDialog
Usage information from UseCounter
The usage of showModalDialog has dropped from 0.006% to 0.0001% since we disabled the API by default (see https://www.chromestatus.com/metrics/feature/timeline/popularity/195
). We know, however, that the API is used in enterprise environments where usage reporting is commonly disabled, so those numbers have to be taken with a grain of salt.
Requesting approval to remove too?