polyfill_detection.js

if (
      typeof window !== 'undefined' &&
      'IntersectionObserver' in window &&
      'IntersectionObserverEntry' in window &&
      'intersectionRatio' in window.IntersectionObserverEntry.prototype
    ) {
      let observer = new IntersectionObserver()
      //rest of the code
    } else {
      import('intersection-observer').then(() => {
        let observer = new IntersectionObserver()
        //rest of code
      })
    }

I put this code in each page or I use only in _app,js?