@indielayer/ui/src/virtual/utils/getRTLOffsetType.ts

Indielayer UI Components with Tailwind CSS build for Vue 3

export type RTLOffsetType =
  | 'negative'
  | 'positive-descending'
  | 'positive-ascending';

let cachedRTLResult: RTLOffsetType | null = null

// TRICKY According to the spec, scrollLeft should be negative for RTL aligned elements.
// Chrome does not seem to adhere; its scrollLeft values are positive (measured relative to the left).
// Safari's elastic bounce makes detecting this even more complicated wrt potential false positives.
// The safest way to check this is to intentionally set a negative offset,
// and then verify that the subsequent "scroll" event matches the negative offset.
// If it does not match, then we can assume a non-standard RTL scroll implementation.
export function getRTLOffsetType(recalculate: boolean = false): RTLOffsetType {
  if (cachedRTLResult === null || recalculate) {
    const outerDiv = document.createElement('div')
    const outerStyle = outerDiv.style

    outerStyle.width = '50px'
    outerStyle.height = '50px'
    outerStyle.overflow = 'scroll'
    outerStyle.direction = 'rtl'

    const innerDiv = document.createElement('div')
    const innerStyle = innerDiv.style

    innerStyle.width = '100px'
    innerStyle.height = '100px'

    outerDiv.appendChild(innerDiv)

    document.body.appendChild(outerDiv)

    if (outerDiv.scrollLeft > 0) {
      cachedRTLResult = 'positive-descending'
    } else {
      outerDiv.scrollLeft = 1
      if (outerDiv.scrollLeft === 0) {
        cachedRTLResult = 'negative'
      } else {
        cachedRTLResult = 'positive-ascending'
      }
    }

    document.body.removeChild(outerDiv)

    return cachedRTLResult
  }

  return cachedRTLResult
}