Function Registry

Lesson Notes

Our function registry

When Barba swaps in a new page, your JavaScript doesn't automatically re-run. The browser already executed your scripts on initial load. The function registry gives you clear moments to reinitialize your code.

function initOnceFunctions() {
  // Runs once on first page load
}

function initBeforeEnterFunctions(next) {
  container = next || document;
  // Runs before the enter animation
}

function initAfterEnterFunctions(next) {
  container = next || document;
  // Runs after enter animation completes
}

When to use which

• ‍initOnceFunctions First page load only. Use it for global stuff outside the container (nav, audio player)
• ‍initBeforeEnterFunctions Before enter animation. Use for things that need to be setup before page is visible.
• ‍initAfterEnterFunctions After transition completes. Most things: sliders, scroll triggers, accordions, video players

Registering your functions

The has() check looks for the element in the current container. If it exists, the function runs. If not, it skips. This makes scaling your project pretty effortless.

function initAfterEnterFunctions(next) {
  container = next || document;

  if (has('[data-accordion]')) initAccordion();
  if (has('[data-something]')) initSomething();
  // Etc...

  lenis.resize();
  ScrollTrigger.refresh();
}

Writing your functions

function initAccordion() {
  const accordions = container.querySelectorAll('[data-accordion]');
  accordions.forEach(accordion => {
    // your accordion logic
  });
}

Query from container to target only the new page content. Use document if you need to query elements outside the Barba container (like modals).

• container scoped to the new page, use for elements inside the Barba container.
• document whole page, use for persistent elements like nav or modals.

Boilerplate

// -----------------------------------------
// OSMO PAGE TRANSITION BOILERPLATE
// -----------------------------------------

gsap.registerPlugin(CustomEase);

history.scrollRestoration = "manual";

let lenis = null;
let nextPage = document;
let onceFunctionsInitialized = false;

const hasLenis = typeof window.Lenis !== "undefined";
const hasScrollTrigger = typeof window.ScrollTrigger !== "undefined";

const rmMQ = window.matchMedia("(prefers-reduced-motion: reduce)");
let reducedMotion = rmMQ.matches;
rmMQ.addEventListener?.("change", e => (reducedMotion = e.matches));
rmMQ.addListener?.(e => (reducedMotion = e.matches)); 

const has = (s) => !!nextPage.querySelector(s);

let staggerDefault = 0.05;
let durationDefault = 0.6;

CustomEase.create("osmo", "0.625, 0.05, 0, 1");
gsap.defaults({ ease: "osmo", duration: durationDefault });



// -----------------------------------------
// FUNCTION REGISTRY
// -----------------------------------------

function initOnceFunctions() {
  initLenis();
  if (onceFunctionsInitialized) return;
  onceFunctionsInitialized = true;
  
  // Runs once on first load
  // if (has('[data-something]')) initSomething();
}

function initBeforeEnterFunctions(next) {
  nextPage = next || document;
  
  // Runs before the enter animation
  // if (has('[data-something]')) initSomething();
}

function initAfterEnterFunctions(next) {
  nextPage = next || document;
  
  // Runs after enter animation completes
  // if (has('[data-something]')) initSomething();
  
  
  if(hasLenis){
    lenis.resize();
  }
  
  if (hasScrollTrigger) {
    ScrollTrigger.refresh();
  }
}



// -----------------------------------------
// PAGE TRANSITIONS
// -----------------------------------------

function runPageOnceAnimation(next) {
  const tl = gsap.timeline();

  tl.call(() => {
    resetPage(next)
  }, null, 0);

  return tl;
}

function runPageLeaveAnimation(current, next) {
  const tl = gsap.timeline({
    onComplete: () => { current.remove() }
  });
  
  if (reducedMotion) {
    // Immediate swap behavior if user prefers reduced motion
    return tl.set(current, { autoAlpha: 0 });
  }

  tl.to(current, { autoAlpha: 0, duration: 0.4 });

  return tl;
}

function runPageEnterAnimation(next){
  const tl = gsap.timeline();
  
  if (reducedMotion) {
    // Immediate swap behavior if user prefers reduced motion
    tl.set(next, { autoAlpha: 1 });
    tl.add("pageReady")
    tl.call(resetPage, [next], "pageReady");
    return new Promise(resolve => tl.call(resolve, null, "pageReady"));
  }
  
  tl.add("startEnter", 0.6);
  
  tl.fromTo(next, {
    autoAlpha: 0,
  },{
    autoAlpha: 1,
  }, "startEnter");

  tl.add("pageReady");
  tl.call(resetPage, [next], "pageReady");

  return new Promise(resolve => {
    tl.call(resolve, null, "pageReady");
  });
}


// -----------------------------------------
// BARBA HOOKS + INIT
// -----------------------------------------

barba.hooks.beforeEnter(data => {
  // Position new container on top
  gsap.set(data.next.container, {
    position: "fixed",
    top: 0,
    left: 0,
    right: 0,
  });
  
  if(hasLenis){
    lenis.stop();
  }
  
  initBeforeEnterFunctions(data.next.container);
  applyThemeFrom(data.next.container);
});

barba.hooks.afterLeave(() => {
  if(hasScrollTrigger){
    ScrollTrigger.getAll().forEach(trigger => trigger.kill());
  }
});

barba.hooks.enter(data => {
  initBarbaNavUpdate(data);
})

barba.hooks.afterEnter(data => {
  // Run page functions
  initAfterEnterFunctions(data.next.container);
  
  // Settle
  if(hasLenis){
    lenis.resize();
    lenis.start();    
  }
  
  if(hasScrollTrigger){
    ScrollTrigger.refresh(); 
  }
});

barba.init({
  debug: true, // Set to 'false' in production
  timeout: 7000,
  preventRunning: true,
  transitions: [
    {
      name: "default",
      sync: true,
      
      // First load
      async once(data) {
        initOnceFunctions();

        return runPageOnceAnimation(data.next.container);
      },

      // Current page leaves
      async leave(data) {
        return runPageLeaveAnimation(data.current.container, data.next.container);
      },

      // New page enters
      async enter(data) {
        return runPageEnterAnimation(data.next.container);
      }
    }
  ],
});



// -----------------------------------------
// GENERIC + HELPERS
// -----------------------------------------

const themeConfig = {
  light: {
    nav: "dark",
    transition: "light"
  },
  dark: {
    nav: "light",
    transition: "dark"
  }
};

function applyThemeFrom(container) {
  const pageTheme = container?.dataset?.pageTheme || "light";
  const config = themeConfig[pageTheme] || themeConfig.light;
  
  document.body.dataset.pageTheme = pageTheme;
  const transitionEl = document.querySelector('[data-theme-transition]');
  if (transitionEl) {
    transitionEl.dataset.themeTransition = config.transition;
  }

  const nav = document.querySelector('[data-theme-nav]');
  if (nav) {
    nav.dataset.themeNav = config.nav;
  }
}

function initLenis() {
  if (lenis) return; // already created
  if (!hasLenis) return;

  lenis = new Lenis({
    lerp: 0.165,
    wheelMultiplier: 1.25,
  });

  if (hasScrollTrigger) {
    lenis.on("scroll", ScrollTrigger.update);
  }

  gsap.ticker.add((time) => {
    lenis.raf(time * 1000);
  });

  gsap.ticker.lagSmoothing(0);
}

function resetPage(container){
  window.scrollTo(0, 0);
  gsap.set(container, { clearProps: "position,top,left,right" });
  
  if(hasLenis){
    lenis.resize();
    lenis.start();    
  }
}

function debounceOnWidthChange(fn, ms) {
  let last = innerWidth,
    timer;
  return function (...args) {
    clearTimeout(timer);
    timer = setTimeout(() => {
      if (innerWidth !== last) {
        last = innerWidth;
        fn.apply(this, args);
      }
    }, ms);
  };
}

function initBarbaNavUpdate(data) {
  var tpl = document.createElement('template');
  tpl.innerHTML = data.next.html.trim();
  var nextNodes = tpl.content.querySelectorAll('[data-barba-update]');
  var currentNodes = document.querySelectorAll('nav [data-barba-update]');

  currentNodes.forEach(function (curr, index) {
    var next = nextNodes[index];
    if (!next) return;

    // Aria-current sync
    var newStatus = next.getAttribute('aria-current');
    if (newStatus !== null) {
      curr.setAttribute('aria-current', newStatus);
    } else {
      curr.removeAttribute('aria-current');
    }

    // Class list sync
    var newClassList = next.getAttribute('class') || '';
    curr.setAttribute('class', newClassList);
  });
}



// -----------------------------------------
// YOUR FUNCTIONS GO BELOW HERE
// -----------------------------------------