submit-social-housing-lettings-and-sales-data/app/webpacker/controllers/numeric_question_controller.js

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  calculateFields() {
    const affectedField = this.element.dataset.target;
    const fieldsToAdd = JSON.parse(this.element.dataset.calculated).map(x => `case-log-${x.replaceAll("_","-")}-field`);
    const valuesToAdd = fieldsToAdd.map(x => document.getElementById(x).value).filter(x => x);
    const newValue =  valuesToAdd.map(x => parseInt(x)).reduce((a, b) => a + b, 0);
    const elementToUpdate = document.getElementById(affectedField);
    elementToUpdate.value = newValue;
  }
}