Decode google encoded polyline

polyline-decode.js

// https://developers.google.com/maps/documentation/utilities/polylinealgorithm
function polylineDecode (str, precision) {
  // Decode str to int array
  let strIndex = 0
  let values = []
  while (strIndex < str.length) {
    let byte
    let result = 0
    let shift = 0
    do {
      byte = str.charCodeAt(strIndex++) - 63
      result |= (byte & 0x1f) << shift
      shift += 5
    } while (byte >= 0x20)
    values.push((result & 1) ? ~(result >> 1) : (result >> 1))
  }

  const factor = Math.pow(10, precision === undefined ? 5 : precision)
  const dim = 2
  let coords = []
  // Deltas -> absolute values
  for (let i = dim; i < values.length; i++) values[i] += values[i - dim]
  // Group & scale
  for (let i = 0; i < values.length; i += dim) coords.push(values.slice(i, i + dim).map(n => n / factor))

  return coords
}