Return inside for loop return initial value

I have a problem to understand why does RETURN in FOR loop returns me always initial fact value (let fact = 1):

const factorial = function(a) {
  let fact=1;
  if(a===0){
    return 1;
  }
  else{
    for(let i=1; i<=a; i++){
      fact*=i;
      return fact;**   // This return
    }
    return fact  
  }
  return fact;  
};


//Result for all values e.g 1,5,10 is always 1, as in initial let fact =1

And when I remove it, my factorial function works totally fine. I have no idea why does it happen:

const factorial = function(a) {
  let fact=1;
  if(a===0){
    return 1;
  }
  else{
    for(let i=1; i<=a; i++){
      fact*=i;
      //Nothing
      }
    return fact  
  }
  return fact;  
};
// Code works fine, I receive factorial correctly

I was expecting to return factorial of my initial value. Instead I receive the initial variable value(1).

If I've understood your question correctly, you are wondering why did you get a return value of 1 in the first code regardless of the input value. That is because you had a return statement inside your for loop, which meant that your for loop would only be entered once and then exited with a return value of 1. Essentially, for loop never iterates, which means that you never get to calculate the value of factorial as fact = 1 * 2 * 3 * ..., you only do the initial step, which is fact = 1.

const factorial = function(a) { // <- you have tested this with 1,5 and 10
  let fact=1;                   // <- here you set fact variable to value of 1
  if(a===0){                    // <- you check if you sent value is equal to 1,
    return 1;                  //     since you have used 1, 5 and 10 you will not be returning a value of 1 here
  }
  else{                        // <- you enter this block of code when the value of a≠0
    for(let i=1; i<=a; i++){   // <- you set the value of i to 1 and you enter the for loop
      fact*=i;                 // <- you multiple your fact value, which is 1, with a value of i, which is also 1, which means you will get fact=1
      return fact;             // <- you return a value of fact, which is 1 here!
    }
    return fact  
  }
  return fact;  
};

return operator does not breaking only for loop: it goes deeper and stops whole function.

So, when you left return inside for without any condition, the return stops whole function at the first iteration of that loop (when fact is 1).

That means, that your code:

const factorial = function(a) {
  let fact=1;
  if(a===0){
    return 1;
  }
  else{
    for(let i=1; i<=a; i++){
      fact*=i;
      return fact; // This return
    }
    return fact  
  }
  return fact;  
};

In fact, is equal to:

const factorial = function(a) {
  let fact=1;

  if (a === 0){
    return 1;
  } else {
    let i = 1;
    fact *= i;
    return fact;
  }
};

Example of valid condition for return operator inside for loop:

function isAnyStringInside(values) {
  for (let i = 0; i < values.length; i += 1) {
    if (typeof values[i] === 'string') {
      return true;
    }
  }

  return false;
}

isAnyStringInside([1,2,3,4,5,'Hello',2,3,4,5]); // true
isAnyStringInside([1,2,3,4,5,2,3,4,5]); // false