improved-redability-updated.js

const makeCoordinatesZeroBased = rawCoordinates => Object.entries(rawCoordinates)
  .reduce((processedCoordinates, [coordinate, value]) => {
    const isCoordinateValid = typeof value === 'number';
    
    let updatedValue = value;
    
    if (isCoordinateValid)
      updatedValue = value - 1;
    
    processedCoordinates[coordinate] = updatedValue;
    
    return processedCoordinates;
  }, {});