How to iterate over a callback n times in JavaScript ?

17 Feb, 2022
Given a callback function we have to iterate over a callback n times. The callback is a function that is passed as an argument. for iterate over callback function, we have to run callback function n time.
Approach 1: We use recursion to iterate n times callback function.
First create callback function factor which takes n as argument.
Factor function generate pattern of n length.
Create test function that takes callback function and n.
Test function checks value of n is equal to 0  and not.
If n is 0 it return terminate test function, else it call callback function which print the pattern.
Example: 
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 loop statement to iterate over callback. 
First we create callback function factor which generate factorial of number.
Create test function with argument n and callback function.
Check value of n if it in invalid terminate if not continue.
Create for loop with range n.
On each loop call callback function which print factorial of each number.
Example:  
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
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