Apply Transform Over Each Element in Array
<p>Given an integer array&nbsp;<code>arr</code>&nbsp;and a mapping function&nbsp;<code>fn</code>, return&nbsp;a new array with a transformation applied to each element.</p>

<p>The returned array should be created such that&nbsp;<code>returnedArray[i] = fn(arr[i], i)</code>.</p>

<p>Please solve it without the built-in <code>Array.map</code> method.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> arr = [1,2,3], fn = function plusone(n) { return n + 1; }
<strong>Output:</strong> [2,3,4]
<strong>Explanation:</strong>
const newArray = map(arr, plusone); // [2,3,4]
The function increases each value in the array by one. 
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> arr = [1,2,3], fn = function plusI(n, i) { return n + i; }
<strong>Output:</strong> [1,3,5]
<strong>Explanation:</strong> The function increases each value by the index it resides in.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> arr = [10,20,30], fn = function constant() { return 42; }
<strong>Output:</strong> [42,42,42]
<strong>Explanation:</strong> The function always returns 42.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= arr.length &lt;= 1000</code></li>
	<li><code><font face="monospace">-10<sup>9</sup>&nbsp;&lt;= arr[i] &lt;= 10<sup>9</sup></font></code></li>
	<li><code>fn</code> returns an integer.</li>
</ul>
JavaScript
function map(arr: number[], fn: (n: number, i: number) => number): number[] {
    for (let i = 0; i < arr.length; ++i) {
        arr[i] = fn(arr[i], i);
    }
    return arr;
}
