# 2635. Apply Transform Over Each Element in Array

###### tags: `leetcode 30 days js challenge` `Easy`

[2635. Apply Transform Over Each Element in Array](https://leetcode.com/problems/apply-transform-over-each-element-in-array/)

### 題目描述

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.

### 範例

**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`
- -10^9^ <= `arr[i]` <= 10^9^
- `fn returns a number`

### 解答

#### TypeScript

function map(arr: number[], fn: (n: number, i: number) => number): number[] {
  const result = [];

  for (let i = 0; i < arr.length; i++) {
    result.push(fn(arr[i], i));
  }

  return result;
}

> [name=Sheep][time=Mon, May 8, 2023]

### Reference

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