Apply Transform Over Each Element in Array 轉換陣列的每個元素

Given an integer array arr and a mapping function fn, return a new array with a transformation applied to each element.

The returned array should be created such that returnedArray[i] = fn(arr[i], i).

Please solve it without the built-in Array.map method.

Example 1:

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

Example 2:

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

Example 3:

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

Constraints:

0 <= arr.length <= 1000
-109 <= arr[i] <= 109
fn returns a number

解法:

這是在講給一個數字的陣列，以及運算的function，這個運算function可以帶入兩個參數，分別是數字跟索引位置，然後回傳一個數字
需求把陣列給個數字都餵給這個function後以這個回傳做為新數字

const map = (arr: number[], fn: (n: number, i: number) => number) => arr.map((num, i)=> fn(num, i));