Answer:
The correct fill in the blanks in the given question is given as 
 var check = num.isInteger(purchase); // giving the input by the user--(1)
       while(!check)  // check the condition .......(2)
       {
check = num.isInteger(purchase);  // taking by the user  in the "num" ..(3)                   
       }
Explanation:
Following are the description of solution 
- In the first statement, we Taking the input in the "check" variable. This statement num.isInteger(purchase); is taking the input and convert this into an "integer" type.
- The while(!check) is checking and controlling the condition of a while loop.
- Finally, we taking the input inside the while loop to regulate the condition of while loop.