intersection observer direction helpers

io.js

let previousY = 0
let previousRatio = 0

function getObserverEntryInfo(entry, previousY, previousRatio) {

  let direction
  let approach

  const hasLargerRatio =
    entry.intersectionRatio > previousRatio

  if (entry.boundingClientRect.y < previousY) {

    direction = 'down'

  }
  else {

    direction = 'up'

  }

  if (direction === 'down') {

    if (hasLargerRatio && entry.isIntersecting) {

      approach = 'entering'

    }
    else {

      approach = 'leaving'

    }

  }

  if (direction === 'up' && entry.isIntersecting) {

    if (hasLargerRatio) {

      approach = 'entering'

    }
    else {

      approach = 'leaving'

    }

  }

  return {
    direction: direction,
    approach: approach
  }

}

function ioCallback(entries) {

  entries.forEach(entry => {

    const info = getObserverEntryInfo(entry)
    const direction = info.direction
    const approach = info.approach
    
    if (direction === 'down' && approach === 'entering') {
      
    }
    
    previousY = currentY
    previousRatio = currentRatio

  })

}