Flattening sub-arrays in an Array

Given an array with multiple subarray elements, the final function needs to flatten the array to ensure that the array does not contain subarrays.

Sample Code:

function flatArr(arr) {
// Enter your logic here...
}

Examples:

Input: [1,2,3,[4,5],['numbers']]
Output: [1,2,3,4,5,'numbers']
Explanation: The sub-array elements have been flattened.

Input: [1,[2,[3],4],5]
Output: [1,2,3,4,5]
Explanation: The sub-array elements have been flattened.