Why is it just pass? i want to know more i need explained

I wrote another answer. But I don't understand this.

although, i run chrome debugger but.. i cant understand well..

result = true
// is passed

i don't understand well.. i submit another answer but i want to know why is it just pass.. i need explain more. and I would like to fix from this code. thank you.

function isPrime(num) {
let result;
for(let i = 1 ; i <= num ; i++) {
  if(num[i] / num[i] === 1 && num[i] / num[i] === num[i]){
    result = true
  } else {
    result = false
  }
}
  return result
}
debugger;
let output = isPrime(2);
console.log(output); // --> true

output = isPrime(6);
console.log(output); // --> false

output = isPrime(17);
console.log(output); // --> true