function pow(x,n)  // <-    
{  // <-      
  let result=1;   // <-      =
  for(let i=0;i<n;i++) {result*=x;}   // <-  
  //  { ... }      
  return result;
}

let x=prompt("x?",''), n=prompt("n?",'') // <--  ,
//              ;
if (n <= 0)  // <-    (n <= 0),       
{   // <-      
  //  -         
  alert(`Power ${n} is not supported, please enter an integer number greater than zero`);
}
else // <-        "} else {"
{
  alert(pow(x,n))  //     ;
}

function pow(x, n) {
  let result = 1;

  for (let i = 0; i < n; i++) {
    result *= x;
  }

  return result;
}

let x = prompt("x?", "");
let n = prompt("n?", "");

if (n <= 0) {
  alert(`Power ${n} is not supported,
    please enter an integer number greater than zero`);
} else {
  alert( pow(x, n) );
}