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# How to iterate over a callback n times in JavaScript ?

• Last Updated : 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

 ``

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

 ``

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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