# 2693. Call Function with Custom Context

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

[2693. Call Function with Custom Context](https://leetcode.com/problems/call-function-with-custom-context/)

### 題目描述

Enhance all functions to have the `callPolyfill` method. The method accepts an object `obj` as it's first parameter and any number of additional arguments. The `obj` becomes the `this` context for the function. The additional arguments are passed to the function (that the `callPolyfill` method belongs on).

For example if you had the function:

function tax(price, taxRate) {
  const totalCost = price * (1 + taxRate);
  console.log(`The cost of ${this.item} is ${totalCost}`);
}

Calling this function like `tax(10, 0.1)` will log `"The cost of undefined is 11"`. This is because the `this` context was not defined.

However, calling the function like `tax.callPolyfill({item: "salad"}, 10, 0.1)` will log `"The cost of salad is 11"`. The `this` context was appropriately set, and the function logged an appropriate output.

Please solve this without using the built-in `Function.call` method.

### 範例

**Example 1:**

Input:
fn = function add(b) {
  return this.a + b;
}
args = [{"a": 5}, 7]
Output: 12
Explanation:
fn.callPolyfill({"a": 5}, 7); // 12
callPolyfill sets the "this" context to {"a": 5}. 7 is passed as an argument.

**Example 2:**

Input: 
fn = function tax(price, taxRate) { 
 return `The cost of the ${this.item} is ${price * taxRate}`; 
}
args = [{"item": "burger"}, 10, 1,1]
Output: "The cost of the burger is 11"
Explanation: callPolyfill sets the "this" context to {"item": "burger"}. 10 and 1.1 are passed as additional arguments.

**Constraints**:

- `typeof args[0] == 'object' and args[0] != null`
- `1 <= args.length <= 100`
- 2 <= `JSON.stringify(args[0]).length` <= 10⁵

### 解答

#### TypeScript

Function.prototype.callPolyfill = function (context, ...args): any {
  // 在這裡 `this` 代表原本的函式
  const originalFunction = this;

  // 回傳一個新的函式，這個新的函式會使用指定的 `context` 作為 `this` 值去呼叫原本的函式
  return (function () {
    return originalFunction.apply(context, args);
  })();
};

> [name=Sheep][time=Tues, May 30, 2023]

### Reference

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