@ocelot-consulting/hummus-toc/src/countPages.js

An extension for HummusJS to add Table of Contents (including bookmarks).

const {verticalMax, verticalMargin, lineSpacing} = require('../config')

module.exports = itemCount => {
  const verticalTextStart = verticalMax - verticalMargin

  let pageSize = 0
  let pages = 1

  for (let i = 0; i < itemCount; i++) {
    const pageIndex = pageSize ? i % pageSize : i
    const verticalOffset = lineSpacing * (pageIndex + 1)
    const verticalLineStart = verticalTextStart - verticalOffset
    if (verticalLineStart <= verticalMargin) {
      pages++
      if (!pageSize) {
        pageSize = i + 1
      }
    }
  }

  return pages
}