Very fast algorithm for the a first approximation of a very large factorial (10 decimals)

factorial.js

function factorial(number) {
  let result = 0;
  for(let i = number; i > 0; --i) {
    result += Math.log10(i);
  }
  return result;
}

function scientific_factorial(number) {
  let fact = factorial(number);
  let value = Math.pow(10, fact%1);
  let exponent = Math.round(fact);
  return [value, exponent];
}

let result = scientific_factorial(100000);
console.log("value:", result[0], "exponent:", result[1]);
console.log(result[0].toString() + "e" + result[1].toString());