https://github.com/google/open-location-code/blob/master/js/src/openlocationcode.js

@node-pluscodes.md

pluscodes

Code from google/open-location-code is not usable in my environment. So I made a simple wrapper.

• npm open-location-code is a bit outdated
• there is also janne/pluscodes is fairly awesome - has one dependency, doesn't do grid refinement to 11 digits

encode and decode are only methods in index. They ruturn false instead of throwing error

yarn add gist:70446302e9c04d29713c96cb94c55e3f

const { decode, encode } = require("node-pluscodes")

or just skip the wrapper

const OpenLocationCode = require("node-pluscodes/openlocationcode")

const area = OpenLocationCode.decode('8FVC9G8F+6X')

index.js

const OpenLocationCode = require("./openlocationcode")

module.exports = {
  OpenLocationCode,
  encode: ({ latitude, longitude, codeLength }, callback) => {
    // ?? if (callback) callback(false, result)
    try {
      return OpenLocationCode.encode(latitude, longitude, codeLength)
    } catch (error) {
      return false // { error }
    }
  },
  decode: plusCode => {
    try {
      return OpenLocationCode.decode(plusCode)
    } catch (error) {
      return false // { error }
    }
  },
  decodePromise: plusCode =>
    new Promise((resolve, reject) => {
      try {
        const result = OpenLocationCode.decode(plusCode)
        resolve(result)
      } catch (error) {
        reject(error)
      }
    }),
  encodePromise: ({ latitude, longitude, codeLength }) =>
    new Promise((resolve, reject) => {
      try {
        const result = OpenLocationCode.encode(latitude, longitude, codeLength)
        resolve(result)
      } catch (error) {
        reject(error)
      }
    }),
}

openlocationcode.js

// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the 'License');
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an 'AS IS' BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * Convert locations to and from short codes.
 *
 * Open Location Codes are short, 10-11 character codes that can be used instead
 * of street addresses. The codes can be generated and decoded offline, and use
 * a reduced character set that minimises the chance of codes including words.
 *
 * Codes are able to be shortened relative to a nearby location. This means that
 * in many cases, only four to seven characters of the code are needed.
 * To recover the original code, the same location is not required, as long as
 * a nearby location is provided.
 *
 * Codes represent rectangular areas rather than points, and the longer the
 * code, the smaller the area. A 10 character code represents a 13.5x13.5
 * meter area (at the equator. An 11 character code represents approximately
 * a 2.8x3.5 meter area.
 *
 * Two encoding algorithms are used. The first 10 characters are pairs of
 * characters, one for latitude and one for latitude, using base 20. Each pair
 * reduces the area of the code by a factor of 400. Only even code lengths are
 * sensible, since an odd-numbered length would have sides in a ratio of 20:1.
 *
 * At position 11, the algorithm changes so that each character selects one
 * position from a 4x5 grid. This allows single-character refinements.
 *
 * Examples:
 *
 *   Encode a location, default accuracy:
 *   var code = OpenLocationCode.encode(47.365590, 8.524997);
 *
 *   Encode a location using one stage of additional refinement:
 *   var code = OpenLocationCode.encode(47.365590, 8.524997, 11);
 *
 *   Decode a full code:
 *   var coord = OpenLocationCode.decode(code);
 *   var msg = 'Center is ' + coord.latitudeCenter + ',' + coord.longitudeCenter;
 *
 *   Attempt to trim the first characters from a code:
 *   var shortCode = OpenLocationCode.shorten('8FVC9G8F+6X', 47.5, 8.5);
 *
 *   Recover the full code from a short code:
 *   var code = OpenLocationCode.recoverNearest('9G8F+6X', 47.4, 8.6);
 *   var code = OpenLocationCode.recoverNearest('8F+6X', 47.4, 8.6);
 */
var OpenLocationCode = {}

/**
 * Provides a normal precision code, approximately 14x14 meters.
 * @const {number}
 */
OpenLocationCode.CODE_PRECISION_NORMAL = 10

/**
 * Provides an extra precision code, approximately 2x3 meters.
 * @const {number}
 */
OpenLocationCode.CODE_PRECISION_EXTRA = 11

// A separator used to break the code into two parts to aid memorability.
var SEPARATOR_ = "+"

// The number of characters to place before the separator.
var SEPARATOR_POSITION_ = 8

// The character used to pad codes.
var PADDING_CHARACTER_ = "0"

// The character set used to encode the values.
var CODE_ALPHABET_ = "23456789CFGHJMPQRVWX"

// The base to use to convert numbers to/from.
var ENCODING_BASE_ = CODE_ALPHABET_.length

// The maximum value for latitude in degrees.
var LATITUDE_MAX_ = 90

// The maximum value for longitude in degrees.
var LONGITUDE_MAX_ = 180

// Maximum code length using lat/lng pair encoding. The area of such a
// code is approximately 13x13 meters (at the equator), and should be suitable
// for identifying buildings. This excludes prefix and separator characters.
var PAIR_CODE_LENGTH_ = 10

// The resolution values in degrees for each position in the lat/lng pair
// encoding. These give the place value of each position, and therefore the
// dimensions of the resulting area.
var PAIR_RESOLUTIONS_ = [20.0, 1.0, 0.05, 0.0025, 0.000125]

// Number of columns in the grid refinement method.
var GRID_COLUMNS_ = 4

// Number of rows in the grid refinement method.
var GRID_ROWS_ = 5

// Size of the initial grid in degrees.
var GRID_SIZE_DEGREES_ = 0.000125

// Minimum length of a code that can be shortened.
var MIN_TRIMMABLE_CODE_LEN_ = 6

/**
  Returns the OLC alphabet.
 */
var getAlphabet = (OpenLocationCode.getAlphabet = function() {
  return CODE_ALPHABET_
})

/**
 * Determines if a code is valid.
 *
 * To be valid, all characters must be from the Open Location Code character
 * set with at most one separator. The separator can be in any even-numbered
 * position up to the eighth digit.
 *
 * @param {string} code The string to check.
 * @return {boolean} True if the string is a valid code.
 */
var isValid = (OpenLocationCode.isValid = function(code) {
  if (!code || typeof code !== "string") {
    return false
  }
  // The separator is required.
  if (code.indexOf(SEPARATOR_) == -1) {
    return false
  }
  if (code.indexOf(SEPARATOR_) != code.lastIndexOf(SEPARATOR_)) {
    return false
  }
  // Is it the only character?
  if (code.length == 1) {
    return false
  }
  // Is it in an illegal position?
  if (
    code.indexOf(SEPARATOR_) > SEPARATOR_POSITION_ ||
    code.indexOf(SEPARATOR_) % 2 == 1
  ) {
    return false
  }
  // We can have an even number of padding characters before the separator,
  // but then it must be the final character.
  if (code.indexOf(PADDING_CHARACTER_) > -1) {
    // Not allowed to start with them!
    if (code.indexOf(PADDING_CHARACTER_) == 0) {
      return false
    }
    // There can only be one group and it must have even length.
    var padMatch = code.match(new RegExp("(" + PADDING_CHARACTER_ + "+)", "g"))
    if (
      padMatch.length > 1 ||
      padMatch[0].length % 2 == 1 ||
      padMatch[0].length > SEPARATOR_POSITION_ - 2
    ) {
      return false
    }
    // If the code is long enough to end with a separator, make sure it does.
    if (code.charAt(code.length - 1) != SEPARATOR_) {
      return false
    }
  }
  // If there are characters after the separator, make sure there isn't just
  // one of them (not legal).
  if (code.length - code.indexOf(SEPARATOR_) - 1 == 1) {
    return false
  }

  // Strip the separator and any padding characters.
  code = code
    .replace(new RegExp("\\" + SEPARATOR_ + "+"), "")
    .replace(new RegExp(PADDING_CHARACTER_ + "+"), "")
  // Check the code contains only valid characters.
  for (var i = 0, len = code.length; i < len; i++) {
    var character = code.charAt(i).toUpperCase()
    if (character != SEPARATOR_ && CODE_ALPHABET_.indexOf(character) == -1) {
      return false
    }
  }
  return true
})

/**
 * Determines if a code is a valid short code.
 *
 * @param {string} code The string to check.
 * @return {boolean} True if the string can be produced by removing four or
 *     more characters from the start of a valid code.
 */
var isShort = (OpenLocationCode.isShort = function(code) {
  // Check it's valid.
  if (!isValid(code)) {
    return false
  }
  // If there are less characters than expected before the SEPARATOR.
  if (
    code.indexOf(SEPARATOR_) >= 0 &&
    code.indexOf(SEPARATOR_) < SEPARATOR_POSITION_
  ) {
    return true
  }
  return false
})

/**
 * Determines if a code is a valid full Open Location Code.
 *
 * @param {string} code The string to check.
 * @return {boolean} True if the code represents a valid latitude and
 *     longitude combination.
 */
var isFull = (OpenLocationCode.isFull = function(code) {
  if (!isValid(code)) {
    return false
  }
  // If it's short, it's not full.
  if (isShort(code)) {
    return false
  }

  // Work out what the first latitude character indicates for latitude.
  var firstLatValue =
    CODE_ALPHABET_.indexOf(code.charAt(0).toUpperCase()) * ENCODING_BASE_
  if (firstLatValue >= LATITUDE_MAX_ * 2) {
    // The code would decode to a latitude of >= 90 degrees.
    return false
  }
  if (code.length > 1) {
    // Work out what the first longitude character indicates for longitude.
    var firstLngValue =
      CODE_ALPHABET_.indexOf(code.charAt(1).toUpperCase()) * ENCODING_BASE_
    if (firstLngValue >= LONGITUDE_MAX_ * 2) {
      // The code would decode to a longitude of >= 180 degrees.
      return false
    }
  }
  return true
})

/**
 * Encode a location into an Open Location Code.
 *
 * @param {number} latitude The latitude in signed decimal degrees. It will
 *     be clipped to the range -90 to 90.
 * @param {number} longitude The longitude in signed decimal degrees. Will be
 *     normalised to the range -180 to 180.
 * @param {?number} codeLength The length of the code to generate. If
 *     omitted, the value OpenLocationCode.CODE_PRECISION_NORMAL will be used.
 *     For a more precise result, OpenLocationCode.CODE_PRECISION_EXTRA is
 *     recommended.
 * @return {string} The code.
 * @throws {Exception} if any of the input values are not numbers.
 */
var encode = (OpenLocationCode.encode = function(
  latitude,
  longitude,
  codeLength
) {
  latitude = Number(latitude)
  longitude = Number(longitude)
  if (typeof codeLength == "undefined") {
    codeLength = OpenLocationCode.CODE_PRECISION_NORMAL
  } else {
    codeLength = Number(codeLength)
  }
  if (isNaN(latitude) || isNaN(longitude) || isNaN(codeLength)) {
    throw "ValueError: Parameters are not numbers"
  }
  if (
    codeLength < 2 ||
    (codeLength < PAIR_CODE_LENGTH_ && codeLength % 2 == 1)
  ) {
    throw "IllegalArgumentException: Invalid Open Location Code length"
  }
  // Ensure that latitude and longitude are valid.
  latitude = clipLatitude(latitude)
  longitude = normalizeLongitude(longitude)
  // Latitude 90 needs to be adjusted to be just less, so the returned code
  // can also be decoded.
  if (latitude == 90) {
    latitude = latitude - computeLatitudePrecision(codeLength)
  }
  var code = encodePairs(
    latitude,
    longitude,
    Math.min(codeLength, PAIR_CODE_LENGTH_)
  )
  // If the requested length indicates we want grid refined codes.
  if (codeLength > PAIR_CODE_LENGTH_) {
    code += encodeGrid(latitude, longitude, codeLength - PAIR_CODE_LENGTH_)
  }
  return code
})

/**
 * Decodes an Open Location Code into its location coordinates.
 *
 * Returns a CodeArea object that includes the coordinates of the bounding
 * box - the lower left, center and upper right.
 *
 * @param {string} code The code to decode.
 * @return {OpenLocationCode.CodeArea} An object with the coordinates of the
 *     area of the code.
 * @throws {Exception} If the code is not valid.
 */
var decode = (OpenLocationCode.decode = function(code) {
  if (!isFull(code)) {
    throw "IllegalArgumentException: " +
      "Passed Open Location Code is not a valid full code: " +
      code
  }
  // Strip out separator character (we've already established the code is
  // valid so the maximum is one), padding characters and convert to upper
  // case.
  code = code.replace(SEPARATOR_, "")
  code = code.replace(new RegExp(PADDING_CHARACTER_ + "+"), "")
  code = code.toUpperCase()
  // Decode the lat/lng pair component.
  var codeArea = decodePairs(code.substring(0, PAIR_CODE_LENGTH_))
  // If there is a grid refinement component, decode that.
  if (code.length <= PAIR_CODE_LENGTH_) {
    return codeArea
  }
  var gridArea = decodeGrid(code.substring(PAIR_CODE_LENGTH_))
  return CodeArea(
    codeArea.latitudeLo + gridArea.latitudeLo,
    codeArea.longitudeLo + gridArea.longitudeLo,
    codeArea.latitudeLo + gridArea.latitudeHi,
    codeArea.longitudeLo + gridArea.longitudeHi,
    codeArea.codeLength + gridArea.codeLength
  )
})

/**
 * Recover the nearest matching code to a specified location.
 *
 * Given a valid short Open Location Code this recovers the nearest matching
 * full code to the specified location.
 *
 * @param {string} shortCode A valid short code.
 * @param {number} referenceLatitude The latitude to use for the reference
 *     location.
 * @param {number} referenceLongitude The longitude to use for the reference
 *     location.
 * @return {string} The nearest matching full code to the reference location.
 * @throws {Exception} if the short code is not valid, or the reference
 *     position values are not numbers.
 */
var recoverNearest = (OpenLocationCode.recoverNearest = function(
  shortCode,
  referenceLatitude,
  referenceLongitude
) {
  if (!isShort(shortCode)) {
    if (isFull(shortCode)) {
      return shortCode
    } else {
      throw "ValueError: Passed short code is not valid: " + shortCode
    }
  }
  referenceLatitude = Number(referenceLatitude)
  referenceLongitude = Number(referenceLongitude)
  if (isNaN(referenceLatitude) || isNaN(referenceLongitude)) {
    throw "ValueError: Reference position are not numbers"
  }
  // Ensure that latitude and longitude are valid.
  referenceLatitude = clipLatitude(referenceLatitude)
  referenceLongitude = normalizeLongitude(referenceLongitude)

  // Clean up the passed code.
  shortCode = shortCode.toUpperCase()
  // Compute the number of digits we need to recover.
  var paddingLength = SEPARATOR_POSITION_ - shortCode.indexOf(SEPARATOR_)
  // The resolution (height and width) of the padded area in degrees.
  var resolution = Math.pow(20, 2 - paddingLength / 2)
  // Distance from the center to an edge (in degrees).
  var halfResolution = resolution / 2.0

  // Use the reference location to pad the supplied short code and decode it.
  var codeArea = decode(
    encode(referenceLatitude, referenceLongitude).substr(0, paddingLength) +
      shortCode
  )
  // How many degrees latitude is the code from the reference? If it is more
  // than half the resolution, we need to move it north or south but keep it
  // within -90 to 90 degrees.
  if (
    referenceLatitude + halfResolution < codeArea.latitudeCenter &&
    codeArea.latitudeCenter - resolution >= -LATITUDE_MAX_
  ) {
    // If the proposed code is more than half a cell north of the reference location,
    // it's too far, and the best match will be one cell south.
    codeArea.latitudeCenter -= resolution
  } else if (
    referenceLatitude - halfResolution > codeArea.latitudeCenter &&
    codeArea.latitudeCenter + resolution <= LATITUDE_MAX_
  ) {
    // If the proposed code is more than half a cell south of the reference location,
    // it's too far, and the best match will be one cell north.
    codeArea.latitudeCenter += resolution
  }

  // How many degrees longitude is the code from the reference?
  if (referenceLongitude + halfResolution < codeArea.longitudeCenter) {
    codeArea.longitudeCenter -= resolution
  } else if (referenceLongitude - halfResolution > codeArea.longitudeCenter) {
    codeArea.longitudeCenter += resolution
  }

  return encode(
    codeArea.latitudeCenter,
    codeArea.longitudeCenter,
    codeArea.codeLength
  )
})

/**
 * Remove characters from the start of an OLC code.
 *
 * This uses a reference location to determine how many initial characters
 * can be removed from the OLC code. The number of characters that can be
 * removed depends on the distance between the code center and the reference
 * location.
 *
 * @param {string} code The full code to shorten.
 * @param {number} latitude The latitude to use for the reference location.
 * @param {number} longitude The longitude to use for the reference location.
 * @return {string} The code, shortened as much as possible that it is still
 *     the closest matching code to the reference location.
 * @throws {Exception} if the passed code is not a valid full code or the
 *     reference location values are not numbers.
 */
var shorten = (OpenLocationCode.shorten = function(code, latitude, longitude) {
  if (!isFull(code)) {
    throw "ValueError: Passed code is not valid and full: " + code
  }
  if (code.indexOf(PADDING_CHARACTER_) != -1) {
    throw "ValueError: Cannot shorten padded codes: " + code
  }
  var code = code.toUpperCase()
  var codeArea = decode(code)
  if (codeArea.codeLength < MIN_TRIMMABLE_CODE_LEN_) {
    throw "ValueError: Code length must be at least " + MIN_TRIMMABLE_CODE_LEN_
  }
  // Ensure that latitude and longitude are valid.
  latitude = Number(latitude)
  longitude = Number(longitude)
  if (isNaN(latitude) || isNaN(longitude)) {
    throw "ValueError: Reference position are not numbers"
  }
  latitude = clipLatitude(latitude)
  longitude = normalizeLongitude(longitude)
  // How close are the latitude and longitude to the code center.
  var range = Math.max(
    Math.abs(codeArea.latitudeCenter - latitude),
    Math.abs(codeArea.longitudeCenter - longitude)
  )
  for (var i = PAIR_RESOLUTIONS_.length - 2; i >= 1; i--) {
    // Check if we're close enough to shorten. The range must be less than 1/2
    // the resolution to shorten at all, and we want to allow some safety, so
    // use 0.3 instead of 0.5 as a multiplier.
    if (range < PAIR_RESOLUTIONS_[i] * 0.3) {
      // Trim it.
      return code.substring((i + 1) * 2)
    }
  }
  return code
})

/**
 * Clip a latitude into the range -90 to 90.
 *
 * @param {number} latitude
 * @return {number} The latitude value clipped to be in the range.
 */
var clipLatitude = function(latitude) {
  return Math.min(90, Math.max(-90, latitude))
}

/**
 * Compute the latitude precision value for a given code length.
 * Lengths <= 10 have the same precision for latitude and longitude, but
 * lengths > 10 have different precisions due to the grid method having
 * fewer columns than rows.
 * @param {number} codeLength
 * @return {number} The latitude precision in degrees.
 */
var computeLatitudePrecision = function(codeLength) {
  if (codeLength <= 10) {
    return Math.pow(20, Math.floor(codeLength / -2 + 2))
  }
  return Math.pow(20, -3) / Math.pow(GRID_ROWS_, codeLength - 10)
}

/**
 * Normalize a longitude into the range -180 to 180, not including 180.
 *
 * @param {number} longitude
 * @return {number} Normalized into the range -180 to 180.
 */
var normalizeLongitude = function(longitude) {
  while (longitude < -180) {
    longitude = longitude + 360
  }
  while (longitude >= 180) {
    longitude = longitude - 360
  }
  return longitude
}

/**
 * Encode a location into a sequence of OLC lat/lng pairs.
 *
 * This uses pairs of characters (longitude and latitude in that order) to
 * represent each step in a 20x20 grid. Each code, therefore, has 1/400th
 * the area of the previous code.
 *
 * This algorithm is used up to 10 digits.
 *
 * @param {number} latitude The location to encode.
 * @param {number} longitude The location to encode.
 * @param {number} codeLength Requested code length.
 * @return {string} The up to 10-digit OLC code for the location.
 */
var encodePairs = function(latitude, longitude, codeLength) {
  var code = ""
  // Adjust latitude and longitude so they fall into positive ranges.
  var adjustedLatitude = latitude + LATITUDE_MAX_
  var adjustedLongitude = longitude + LONGITUDE_MAX_
  // Count digits - can't use string length because it may include a separator
  // character.
  var digitCount = 0
  while (digitCount < codeLength) {
    // Provides the value of digits in this place in decimal degrees.
    var placeValue = PAIR_RESOLUTIONS_[Math.floor(digitCount / 2)]
    // Do the latitude - gets the digit for this place and subtracts that for
    // the next digit.
    var digitValue = Math.floor(adjustedLatitude / placeValue)
    adjustedLatitude -= digitValue * placeValue
    code += CODE_ALPHABET_.charAt(digitValue)
    digitCount += 1
    // And do the longitude - gets the digit for this place and subtracts that
    // for the next digit.
    digitValue = Math.floor(adjustedLongitude / placeValue)
    adjustedLongitude -= digitValue * placeValue
    code += CODE_ALPHABET_.charAt(digitValue)
    digitCount += 1
    // Should we add a separator here?
    if (digitCount == SEPARATOR_POSITION_ && digitCount < codeLength) {
      code += SEPARATOR_
    }
  }
  if (code.length < SEPARATOR_POSITION_) {
    code =
      code +
      Array(SEPARATOR_POSITION_ - code.length + 1).join(PADDING_CHARACTER_)
  }
  if (code.length == SEPARATOR_POSITION_) {
    code = code + SEPARATOR_
  }
  return code
}

/**
 * Encode a location using the grid refinement method into an OLC string.
 *
 * The grid refinement method divides the area into a grid of 4x5, and uses a
 * single character to refine the area. This allows default accuracy OLC codes
 * to be refined with just a single character.
 *
 * This algorithm is used for codes longer than 10 digits.
 *
 * @param {number} latitude The location to encode.
 * @param {number} longitude The location to encode.
 * @param {number} codeLength Requested code length.
 * @return {string} The OLC code digits from the 11th digit on.
 */
var encodeGrid = function(latitude, longitude, codeLength) {
  var code = ""
  var latPlaceValue = GRID_SIZE_DEGREES_
  var lngPlaceValue = GRID_SIZE_DEGREES_
  // Adjust latitude and longitude so they fall into positive ranges and
  // get the offset for the required places.
  latitude += LATITUDE_MAX_
  longitude += LONGITUDE_MAX_
  // To avoid problems with floating point, get rid of the degrees.
  latitude = latitude % 1.0
  longitude = longitude % 1.0
  var adjustedLatitude = latitude % latPlaceValue
  var adjustedLongitude = longitude % lngPlaceValue
  for (var i = 0; i < codeLength; i++) {
    // Work out the row and column.
    var row = Math.floor(adjustedLatitude / (latPlaceValue / GRID_ROWS_))
    var col = Math.floor(adjustedLongitude / (lngPlaceValue / GRID_COLUMNS_))
    latPlaceValue /= GRID_ROWS_
    lngPlaceValue /= GRID_COLUMNS_
    adjustedLatitude -= row * latPlaceValue
    adjustedLongitude -= col * lngPlaceValue
    code += CODE_ALPHABET_.charAt(row * GRID_COLUMNS_ + col)
  }
  return code
}

/**
 * Decode an OLC code made up of lat/lng pairs.
 *
 * This decodes an OLC code made up of alternating latitude and longitude
 * characters, encoded using base 20.
 *
 * @param {string} code The code to decode, assumed to be a valid full code,
 *     but with the separator removed.
 * @return {OpenLocationCode.CodeArea} The code area object.
 */
var decodePairs = function(code) {
  // Get the latitude and longitude values. These will need correcting from
  // positive ranges.
  var latitude = decodePairsSequence(code, 0)
  var longitude = decodePairsSequence(code, 1)
  // Correct the values and set them into the CodeArea object.
  return new CodeArea(
    latitude[0] - LATITUDE_MAX_,
    longitude[0] - LONGITUDE_MAX_,
    latitude[1] - LATITUDE_MAX_,
    longitude[1] - LONGITUDE_MAX_,
    code.length
  )
}

/**
 * Decode either a latitude or longitude sequence.
 *
 * This decodes the latitude or longitude sequence of a lat/lng pair encoding.
 * Starting at the character at position offset, every second character is
 * decoded and the value returned.
 *
 * @param {string} code A valid full OLC code, with the separator removed.
 * @param {string} offset The character to start from.
 * @return {[number]} An array of two numbers, representing the lower and
 *     upper range in decimal degrees. These are in positive ranges and will
 *     need to be corrected appropriately.
 */
var decodePairsSequence = function(code, offset) {
  var i = 0
  var value = 0
  while (i * 2 + offset < code.length) {
    value +=
      CODE_ALPHABET_.indexOf(code.charAt(i * 2 + offset)) * PAIR_RESOLUTIONS_[i]
    i += 1
  }
  return [value, value + PAIR_RESOLUTIONS_[i - 1]]
}

/**
 * Decode the grid refinement portion of an OLC code.
 *
 * @param {string} code The grid refinement section of a code.
 * @return {OpenLocationCode.CodeArea} The area of the code.
 */
var decodeGrid = function(code) {
  var latitudeLo = 0.0
  var longitudeLo = 0.0
  var latPlaceValue = GRID_SIZE_DEGREES_
  var lngPlaceValue = GRID_SIZE_DEGREES_
  var i = 0
  while (i < code.length) {
    var codeIndex = CODE_ALPHABET_.indexOf(code.charAt(i))
    var row = Math.floor(codeIndex / GRID_COLUMNS_)
    var col = codeIndex % GRID_COLUMNS_

    latPlaceValue /= GRID_ROWS_
    lngPlaceValue /= GRID_COLUMNS_

    latitudeLo += row * latPlaceValue
    longitudeLo += col * lngPlaceValue
    i += 1
  }
  return CodeArea(
    latitudeLo,
    longitudeLo,
    latitudeLo + latPlaceValue,
    longitudeLo + lngPlaceValue,
    code.length
  )
}

/**
 * Coordinates of a decoded Open Location Code.
 *
 * The coordinates include the latitude and longitude of the lower left and
 * upper right corners and the center of the bounding box for the area the
 * code represents.
 *
 * @constructor
 */
var CodeArea = (OpenLocationCode.CodeArea = function(
  latitudeLo,
  longitudeLo,
  latitudeHi,
  longitudeHi,
  codeLength
) {
  return new OpenLocationCode.CodeArea.fn.init(
    latitudeLo,
    longitudeLo,
    latitudeHi,
    longitudeHi,
    codeLength
  )
})
CodeArea.fn = CodeArea.prototype = {
  init: function(latitudeLo, longitudeLo, latitudeHi, longitudeHi, codeLength) {
    /**
     * The latitude of the SW corner.
     * @type {number}
     */
    this.latitudeLo = latitudeLo
    /**
     * The longitude of the SW corner in degrees.
     * @type {number}
     */
    this.longitudeLo = longitudeLo
    /**
     * The latitude of the NE corner in degrees.
     * @type {number}
     */
    this.latitudeHi = latitudeHi
    /**
     * The longitude of the NE corner in degrees.
     * @type {number}
     */
    this.longitudeHi = longitudeHi
    /**
     * The number of digits in the code.
     * @type {number}
     */
    this.codeLength = codeLength
    /**
     * The latitude of the center in degrees.
     * @type {number}
     */
    this.latitudeCenter = Math.min(
      latitudeLo + (latitudeHi - latitudeLo) / 2,
      LATITUDE_MAX_
    )
    /**
     * The longitude of the center in degrees.
     * @type {number}
     */
    this.longitudeCenter = Math.min(
      longitudeLo + (longitudeHi - longitudeLo) / 2,
      LONGITUDE_MAX_
    )
  },
}
CodeArea.fn.init.prototype = CodeArea.fn

module.exports = OpenLocationCode

package.json

{
  "name": "node-pluscodes",
  "version": "1.0.0",
  "description": "Library to convert between lat/lng and OLC codes",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "Apache-2.0"
}