Updating entries in a JSON file
const fs = require('fs');
// Read data from JSON file and parse it as a JSON object
const dataFromFile = JSON.parse(fs.readFileSync('./Data.json', 'utf8'));

const data = {
  'A0_Water': 'c_inh2o_A0',
  'A1_Water': 'c_inh2o_A1',
  'A2_Water': 'c_inh2o_A2',
  'A3_Water': 'c_inh2o_A3',
  'Barometer': 'b_mbar_corrected',
  'Temp': 'b_temp'
};

// Now for every 'property' in your 'data' object here,
// you need to update the 'dataFromFile' object

for(let property in data) {
  if(data.hasOwnProperty(property)) {
    dataFromFile[property] = data[property];
  }
}

// Write the updated data in the JSON file
fs.writeFileSync('./Data.json', JSON.stringify(dataFromFile));


NOTE: The above code will add a new value in the JSON file if a corresponding key is not found in your data object. You may want to add a check as:

for(let property in data) {
  if(data.hasOwnProperty(property)) {
    if(dataFromFile[property]) {
      dataFromFile[property] = data[property];
    }
  }
}


Now, the update will be preformed only when a corresponding key has been found.