owtlab-tracking/lib/helpers/getScrollState.js

A simple Tracking system

import extend from 'keen-core/lib/utils/extend';

export function getScrollState(obj) {
  const config = typeof obj === 'object' ? obj : {};
  const state = extend(
    {
      pixel: 0,
      pixel_max: 0,
      ratio: null,
      ratio_max: null,
    },
    config,
  );

  if (typeof window !== undefined || typeof document !== undefined) {
    state.pixel = getScrollOffset() + getWindowHeight();
    if (state.pixel > state.pixel_max) {
      state.pixel_max = state.pixel;
    }
    state.ratio = parseFloat(Number(state.pixel / getScrollableArea()).toFixed(2));
    state.ratio_max = parseFloat(Number(state.pixel_max / getScrollableArea()).toFixed(2));
  }

  return state;
}

function getScrollableArea() {
  const { body } = document;
  const html = document.documentElement;
  return (
    Math.max(
      body.scrollHeight,
      body.offsetHeight,
      html.clientHeight,
      html.scrollHeight,
      html.offsetHeight,
    ) || null
  );
}

function getScrollOffset() {
  return window.pageYOffset !== undefined
    ? window.pageYOffset
    : (document.documentElement || document.body.parentNode || document.body)
      .scrollTop;
}

function getWindowHeight() {
  return window.innerHeight || document.documentElement.clientHeight;
}