while(condition) { 
   // statements if the condition is true 
}

var num:number = 5; 
var factorial:number = 1; 

while(num >=1) { 
   factorial = factorial * num; 
   num--; 
} 
console.log("The factorial  is "+factorial);

//Generated by typescript 1.8.10
var num = 5;
var factorial = 1;
while (num >= 1) {
   factorial = factorial * num;
   num--;
}
console.log("The factorial  is " + factorial);

The factorial is 120