code: function getVertexCode(weight, threshold) {
    // threshold must be a single value or a range (array of size 2)
  
    // Iso-bands
    if (Array.isArray(threshold)) {
      if (weight < threshold[0]) {
        return 0;
      }
      return weight < threshold[1] ? 1 : 2;
    }
    // Iso-lines
    return weight >= threshold ? 1 : 0;
  }
docs: Utility methods