Rails add hidden param on submit

Question

I have a Ruby on Rails 4.0 application and I am wondering is it possible to pass a hidden param with JS to a form on form submit in Rails?

Answer 1

The way I would do this is to actually apply it in the controller (not JS):

#app/controllers/your_controller.rb
def create
   @model = Model.new(controller_params)
   @model.save
end

private

def controller_params
   params.require(:controller).permit(:params).merge(param: "value")
end

---

Update

In light of your comment, you'd be able to use the .on("submit") function in JS like this:

#app/assets/javascripts/application.js
$(document).on("submit", "#form", function(){
    // append your params in here
});

As for adding the params, you could benefit from this: Adding POST parameters before submit

$('#commentForm').submit(function(){ //listen for submit event
    $.each(params, function(i,param){
        $('<input />').attr('type', 'hidden')
            .attr('name', param.name)
            .attr('value', param.value)
            .appendTo('#commentForm');
    });

    return true;
});

Answer 2

Why not just add a hidden field in your form that has a default value? With simple_form and haml it will look like this:

= f.input :field, as: :hidden, default: :value