findCulprits.js

// Author: Josh Comeau 
// https://courses.joshwcomeau.com/css-for-js/

// Helps developers finding the parent element that break the fixed position


// Replace “.the-fixed-child” for a CSS selector
// that matches the fixed-position element:
const selector = '.the-fixed-child';

function findCulprits(elem) {
  if (!elem) {
    throw new Error(
      'Could not find element with that selector'
    );
  }

  let parent = elem.parentElement;

  while (parent) {
    const {
      transform,
      willChange,
      filter,
    } = getComputedStyle(parent);

    if (
      transform !== 'none' ||
      willChange === 'transform' ||
      filter !== 'none'
    ) {
      console.warn(
        '🚨 Found a culprit! 🚨\n',
        parent,
        { transform, willChange, filter }
      );
    }
    parent = parent.parentElement;
  }
}

findCulprits(document.querySelector(selector));