在Rails 6上呈现js.erb视图

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def check_username
    @username = params[:username]
    @user_exists = User.exists?(username: @username)
    respond_to do |format|
      format.js
    end
  end
end

# config/routes.rb
Rails.application.routes.draw do
  get 'check_username', to: 'users#check_username'
end

<!-- app/views/users/check_username.js.erb -->
<% if @user_exists %>
  alert("用户名已被占用！");
<% else %>
  alert("用户名可用！");
<% end %>

<!-- app/views/users/new.html.erb -->
<%= form_with model: @user, local: true do |form| %>
  <%= form.label :username %>
  <%= form.text_field :username, id: 'username' %>
  <%= form.submit %>
<% end %>

<script>
  document.getElementById('username').addEventListener('input', function() {
    var username = this.value;
    fetch('/check_username?username=' + encodeURIComponent(username))
      .then(response => response.text())
      .then(data => eval(data));
  });
</script>