roll20-character-sheets/backbone/source/scaffold/tabs/tabs.js

/**
 * The default tab navigation function of the K-scaffold. Courtesy of Riernar. It will add `k-active-tab` to the active tab-container and `k-active-button` to the active button. You can either write your own CSS to control display of these, or use the default CSS included in `scaffold/_k.scss`. Note that `k-active-button` has no default CSS as it is assumed that you will want to style the active button to match your system.
 * @param {Object} trigger - The trigger object
 */
const kSwitchTab = function ({ trigger, attributes, sections, casc }) {
  const [container, tab] = (
    trigger.name.match(/nav-tabs-(.+)--(.+)/) ||
    []
  ).slice(1);
  $20(`[data-container-tab="${container}"]`).removeClass('k-active-tab');
  $20(`[data-container-tab="${container}"][data-tab="${tab}"]`).addClass('k-active-tab');
  $20(`[data-container-button="${container}"]`).removeClass('k-active-button');
  $20(`[data-container-button="${container}"][data-button="${tab}"]`).addClass('k-active-button');
  const tabInputName = `${container.replace(/\-/g,'_')}_tab`;
  if(persistentTabs.indexOf(tabInputName) > -1){
    attributes[tabInputName] = trigger.name;
  }
  if(trigger && trigger.navFuncs){
    trigger.navFuncs.forEach((funcName) => {
      if(funcs[funcName]){
        funcs[funcName]({attributes,sections,casc,trigger});
      }
    });
  }
}

registerFuncs({ kSwitchTab });

/**
 * Sets persistent tabs to their last active state
 * @param {object} trigger - The trigger that caused the function to be called
 * @param {object} attributes - The attribute values of the character
 * @param {object[]} sections - All the repeating section IDs
 * @param {object} casc - Expanded cascade object
 */
const kTabOnOpen = function({trigger,attributes,sections,casc}){
  persistentTabs.forEach((tabInput) => {
    const pseudoTrigger = {name:attributes[tabInput]};
    kSwitchTab({trigger:pseudoTrigger, attributes});
  });
};
registerFuncs({ kTabOnOpen },{type:['opener']});