i can't understand parseInt method in this code

Question

code is like that :)

function test3(num) {
  if (num <= 9) {
    return num;
  }
  let rest = 1;
  while (num) {
    rest = rest * (num % 10);
    num = parseInt(num / 10);
  }
  if (rest <= 9) {
    return rest;
  }
  return test3(rest);
}
debugger;
let output = test3(786);
console.log(output); // --> 0

i understand other logic but, i dont understand 'parseInt' how to work parseInt logic ? apparently i m already read mdn, and any stackover flow answer, can't understand well..

Answer 1

parseInt() is being used here to convert a number that may have a fraction after the decimal point into the integer part.

It works because if the argument to parseInt() isn't a string, it's first converted to a string, and then it parses an integer prefix from that. So parseInt(3.14) is equivalent to parseInt('3.14'), which returns 3.

It's equivalent to Math.floor() in this context.