Custom action for SharePoint Online

Hi All, 

I have a requirement where approvers can navigate to the workflow tasksand approve all the tasks in bulk. 
I am thinking writing a custom action as a SharePoint Add-in and I am quite new to Add-in model. 

There are a couple of custom actions in MSDN. 

Custom actions in the SharePoint add-in model 

Create custom actions to deploy with SharePoint Add-ins

Q: How could I select all workflow tasks and delete them if <g class="gr_ gr_492 gr-alert gr_gramm gr_run_anim Grammar only-ins replaceWithoutSep" data-gr-id="492" id="492">user</g> approves this activity? 

Any sample code would be appreciated. 

Thanks!

Sandy