process.js

function mapit(obj, key, value) {
  if (Array.isArray(key)) {
    value.unshift(key);
    key = null;
  }
  var thing = key ? {} : obj;

  var out = value.reduce(function(newObj, item) {
    sExpr(item, newObj);
    return newObj
  }, thing);
  if (key) {
    obj[key] = out;
  }
}

export function sExpr(v, obj) {
  if (!Array.isArray(v)) {
    obj[v] = true;
    return;
  }
  var key = v.shift();
  if (key === 'PARAMETER') {
    key = v.shift();
  }
  if (v.length === 1) {
    if (Array.isArray(v[0])) {
      obj[key] = {};
      sExpr(v[0], obj[key]);
      return;
    }
    obj[key] = v[0];
    return;
  }
  if (!v.length) {
    obj[key] = true;
    return;
  }
  if (key === 'TOWGS84') {
    obj[key] = v;
    return;
  }
  if (key === 'AXIS') {
    if (!(key in obj)) {
      obj[key] = [];
    }
    obj[key].push(v);
    return;
  }
  if (!Array.isArray(key)) {
    obj[key] = {};
  }

  var i;
  switch (key) {
    case 'UNIT':
    case 'PRIMEM':
    case 'VERT_DATUM':
      obj[key] = {
        name: v[0].toLowerCase(),
        convert: v[1]
      };
      if (v.length === 3) {
        sExpr(v[2], obj[key]);
      }
      return;
    case 'SPHEROID':
    case 'ELLIPSOID':
      obj[key] = {
        name: v[0],
        a: v[1],
        rf: v[2]
      };
      if (v.length === 4) {
        sExpr(v[3], obj[key]);
      }
      return;
    case 'EDATUM':
    case 'ENGINEERINGDATUM':
    case 'LOCAL_DATUM':
    case 'DATUM':
    case 'VERT_CS':
    case 'VERTCRS':
    case 'VERTICALCRS':
      v[0] = ['name', v[0]];
      mapit(obj, key, v);
      return;
    case 'COMPD_CS':
    case 'COMPOUNDCRS':
    case 'FITTED_CS':
    // the followings are the crs defined in
    // https://github.com/proj4js/proj4js/blob/1da4ed0b865d0fcb51c136090569210cdcc9019e/lib/parseCode.js#L11
    case 'PROJECTEDCRS':
    case 'PROJCRS':
    case 'GEOGCS':
    case 'GEOCCS':
    case 'PROJCS':
    case 'LOCAL_CS':
    case 'GEODCRS':
    case 'GEODETICCRS':
    case 'GEODETICDATUM':
    case 'ENGCRS':
    case 'ENGINEERINGCRS':
      v[0] = ['name', v[0]];
      mapit(obj, key, v);
      obj[key].type = key;
      return;
    default:
      i = -1;
      while (++i < v.length) {
        if (!Array.isArray(v[i])) {
          return sExpr(v, obj[key]);
        }
      }
      return mapit(obj, key, v);
  }
}