How to iterate over a callback n times in JavaScript ?

Given a callback function, we have to iterate over a callback n times. The callback is a function that is passed as an argument. To iterate over the callback function, we have to run the callback function n time.

Approach 1: We use recursion to iterate the n times callback function.

• First, create a callback function factor that takes n as an argument.
• The factor function generates a pattern of n length.
• Create a test function that takes a callback function and n.
• The test function checks the value of n is equal to 0  and not.
• If n is 0 it returns the terminate test function, else it calls the callback function which prints the pattern.

Example: This example uses the above approach.

Javascript

<script>
    // callback function that print pattern
    function factor(n) {
      // base case for recursion
      if (n <= 1) {
        console.log("0" + n);
        return;
      }
      // string to store patterns
      let str = "";
      // loop for generate pattern
      for (let i = 1; i <= n; i++) {
        str += `0${i} `;
      }
      // printing patterns
      console.log(str);

      // recursion call with decrement by 1
      return factor(n - 1);
    }

    // function to run callback function
    function test(n, callback) {
      if (n == 0) {
        console.log("please provide value n greater than 0");
        return;
      }

      let k = n;
      //calling callback function
      callback(k);
    }

    // initialising test number
    let t_number = 4;
    // calling main function to call callback function
    test(t_number, factor);
</script>

Output:

01 02 03 04
01 02 03
01 02
01

Approach 2: We use a loop statement to iterate over the callback. 

• First, we create a callback function factor which generates a factorial of numbers.
• Create a test function with argument n and a callback function.
• Check the value of n if it is invalid terminate if not continue.
• Create for loop with range n.
• On each loop call the callback function which prints the factorial of each number.

Example: This example describes the above explained approach.

Javascript

<script>
    // call back function that return factorial
    function factor(number) {
      let j = 1;
      // loop that generate factorial of number
      for (let i = 1; i <= number; i++) {
        j *= i;
      }
      // printing value of factorial
      console.log(`factorial of ${number} is `);
      console.log(j);
    }

    // function that iterate over callback function
    function test(n, callback) {
      if (n <= 0) {
        console.log("invalid number");
        return;
      }
      let k = n;
      // iterating over callback function with for loop
      for (let i = k; i >= 1; i--) callback(i);
    }

    // initialising test variable
    let t_umber = 5;
    // main function calling
    test(t_umber, factor);
</script>

Output:

factorial of 5 is 120
factorial of 4 is 24
factorial of 3 is 6
factorial of 2 is 2 
factorial of 1 is 1