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How to iterate over a callback n times in JavaScript ?

  • Last Updated : 16 Aug, 2021

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.

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  • 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.



  // callback function that print pattern
  function factor(n) {
    // base case for recursion
    if (n <= 1) {
      console.log("0" + n);
    // string to store patterns
    let str = "";
    // loop for generate patter
    for (let i = 1; i <= n; i++) {
      str += `0${i} `;
    // printing patterns
    // 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");
    let k = n;
    //calling callback function
  // initialising test number
  let t_number = 4;
  // calling main function to call callback function
  test(t_number, factor);


01 02 03 04
01 02 03
01 02

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.



  // call back function thar 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 `);
  // function that iterate over callback function
  function test(n, callback) {
    if (n <= 0) {
      console.log("invalide number");
    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);


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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