How do you get the Ruby on Rails generated id of a form element for reference in JavaScript?

Question

When using the form_for helper and a text_field call, Ruby on Rails will generate a unique id for the element that it outp

Answer 1

In case someone has a FormBuilder object from a fields_for block, it is possible to get its id using this snippet:

<%= form.fields_for :something do |fields_form| %>
  <%= fields_form.object_name.gsub(/[\[\]]+/, '_').chop %>id
<% end %>

FieldsForm#object_name returns the field's ID as something like this: user[address][0]. Next, the regex substitution changes groups of one or more brackets to underscores. This substitution leaves a trailing underscore, to which it appends the letters id. For the example provided before, this results in user_address_0_id.