How to add data into the POST method of a form in ExtJS?

When you submit the form set the properties into params: , below I have provided an example:

this.myWindow.get(0).getForm().submit({
  url : 'path_for_action',
  params : {name : value},
  success : function(form, action) {
     // do your stuff here
  },
  failure : function(form, action) {
     // do your stuff here
  }
}

I hope it will be helpful for you.