AEM 6.5 Restrict workflow initiation on assets in assets console

Hi All,

For an asset placed under DAM[say http://localhost:4502/assets.html/content/dam ], for which certain mandatory metadata fields are not provided, we want to prevent user from triggering a workflow from timeline[i.e, on click of "Start" in timeline it should throw alert workflow cannot be started due to mandatory fields not filled and workflow should not get initiated]

Any thoughts on how to do this will be really helpful. Tried looking for some reference code, but could not find any.

Any pointers/reference code will be really helpful.

Below is timeline pic in bottom left corner in http://localhost:4502/assets.html/content/dam from where workflow is initiated, after selection of asset.

arunpatidar26​ Any sample code/reference will be helpful.