Does module pattern in javascript store variables?

const Formatter = (function() {
  let timesRun = 0;
  
  const log = (message) => console.log(`[${Date.now()}] Logger: ${message}`);
  const setTimesRun = () => {
    log("Setting times run");
    ++timesRun;
    console.log(timesRun);
  }

  const makeUppercase = (text) => {
    log("Making uppercase");
    setTimesRun();
    return text.toUpperCase();
  };

  return {
    makeUppercase,
    timesRun,
  }
})()

console.log(Formatter.makeUppercase("tomek"));
console.log(Formatter.timesRun);

console.log(Formatter.makeUppercase("foo"));
console.log(Formatter.timesRun);

console.log(Formatter.makeUppercase("hey"));
console.log(Formatter.timesRun);

With console.log(Formatter.timesRun); I'm expecting the incremented value of timesRun. However, it keeps logging 0. Using console.log(timesRun); inside the setRimesRun() function logs the incremented value. I don't understand where the data is stored and why am I getting 0.

I thought timesRun was always 0 and I added console.log(timesRun); to test it. It showed the incremeneted value which confused the me even more.

Solution

The variable timesRun is locally in the method setTimesRun. You should use the one outside of setTimesRun, so Formatter.timesRun.

You can do like that:

const Formatter = (function() {
  var timesRun = 0;
  const log = (message) => console.log(`[${Date.now()}] Logger: ${message}`);
  const setTimesRun = () => {
    Formatter.timesRun++;
    log("Setting times run to " + timesRun);
    //console.log(timesRun);
  }

  const makeUppercase = (text) => {
    log("Making uppercase");
    setTimesRun();
    return text.toUpperCase();
  };

  return {
    makeUppercase,
    timesRun,
  }
})()

console.log(Formatter.makeUppercase("tomek"));
console.log(Formatter.timesRun);

console.log(Formatter.makeUppercase("foo"));
console.log(Formatter.timesRun);

console.log(Formatter.makeUppercase("hey"));
console.log(Formatter.timesRun);

Here, all times I'm using the same variable: Formatter.timesRun. With this, all logger use the same and will some same instance of this int