Function relative

packages/effect/src/Path.ts:521–611

(from, to)

  },

  relative(from, to) {
    if (from === to) return ""

    from = posixImpl.resolve(from)
    to = posixImpl.resolve(to)

    if (from === to) return ""

    // Trim any leading backslashes
    let fromStart = 1
    for (; fromStart < from.length; ++fromStart) {
      if (from.charCodeAt(fromStart) !== 47 /*/*/) {
        break
      }
    }
    const fromEnd = from.length
    const fromLen = fromEnd - fromStart

    // Trim any leading backslashes
    let toStart = 1
    for (; toStart < to.length; ++toStart) {
      if (to.charCodeAt(toStart) !== 47 /*/*/) {
        break
      }
    }
    const toEnd = to.length
    const toLen = toEnd - toStart

    // Compare paths to find the longest common path from root
    const length = fromLen < toLen ? fromLen : toLen
    let lastCommonSep = -1
    let i = 0
    for (; i <= length; ++i) {
      if (i === length) {
        if (toLen > length) {
          if (to.charCodeAt(toStart + i) === 47 /*/*/) {
            // We get here if `from` is the exact base path for `to`.
            // For example: from='/foo/bar'; to='/foo/bar/baz'
            return to.slice(toStart + i + 1)
          } else if (i === 0) {
            // We get here if `from` is the root
            // For example: from='/'; to='/foo'
            return to.slice(toStart + i)
          }
        } else if (fromLen > length) {
          if (from.charCodeAt(fromStart + i) === 47 /*/*/) {
            // We get here if `to` is the exact base path for `from`.
            // For example: from='/foo/bar/baz'; to='/foo/bar'
            lastCommonSep = i
          } else if (i === 0) {
            // We get here if `to` is the root.
            // For example: from='/foo'; to='/'
            lastCommonSep = 0
          }
        }
        break
      }
      const fromCode = from.charCodeAt(fromStart + i)