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If I read a JSON file by just fs.readFileSync(filename, 'utf-8') it works, but when I add error handling, I get undefined .

const fs = require('fs');
let ruleTemplate;
fs.readFileSync('cmdCreateRule.json', 'utf8', function (err, data) {
  if (err) {
    throw err;
  } else {
    ruleTemplate = JSON.parse(data);
console.log(ruleTempate);
Question
Can anyone see why ruleTemplate becomes undefined?
                You should not supply a callback when calling somethingSync(). It will throw an error if there is a problem even without the callback.
– VLAZ -on strike-
                Jun 22, 2021 at 9:05
readFileSync does not accept a callback function. It only accepts two arguments. The third argument (where you are passing your function which assigns a value to ruleTemplate) is ignored.
readFileSync  returns a string or buffer.
As Quentin said, this is a synchronous function, so it does not get a callback as parameter, try this:
const fs = require('fs');
let ruleTemplate;
try {
  fs.readFileSync('cmdCreateRule.json', 'utf8');
  ruleTemplate = JSON.parse(data);
catch (err) {
  throw err;
console.log(ruleTempate);
        
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